Prepreg comprising polyphenylene ether particles

ABSTRACT

Provided is a prepreg suffering little resin particle fall-off and little resin peeling during prepreg production and during handling in order to have excellent dielectric properties for PPE and favorable adhesiveness. A PPE-containing prepreg constituted of a base material and a curable resin composition including PPE particles, wherein the prepreg is characterized in that (1) PPE extracted from the prepreg using a mixed solvent of toluene and methanol in a mass ratio of 95:5 includes PPE particles (A) insoluble in the mixed solvent, (2) the amount of PPE contained in the PPE particles (A) is 70 mass % or higher, and (3) the number-average molecular weight of the PPE contained in the PPE particles (A) is 8,000-40,000.

TECHNICAL FIELD

The present invention relates to a prepreg comprising polyphenyleneether particles.

BACKGROUND ART

In recent years, with the significant progress in information networktechnology and expanding services that implement information networks,there has been a demand for increased data volumes and faster processingspeeds for electronic devices. Smaller signal wavelengths are effectivefor transferring digital signals in greater volumes and at higherspeeds, and advances are being made toward achieving higher signalfrequencies. Because electrical signals in the high-frequency range tendto decay in wiring circuits, there is a need for electronic circuitboards with high transmission characteristics.

Two approaches are effective for obtaining electronic circuit boardswith high transmission characteristics, namely (i) reducing thedielectric loss tangent of the dielectric material (such as theinsulating resin reinforced in the base material) and (ii) lowering theskin resistance of the conductor (such as metal wiring).

As a method of (i) reducing the dielectric loss tangent of thedielectric material, there is known a method using a low-dielectricresin such as polyphenylene ether (hereunder, PPE) as the insulatingresin. PPE has low permittivity, a low dielectric loss tangent and anexcellent high-frequency characteristic (i.e. dielectriccharacteristic), as well as high heat resistance, and is thereforesuitable as an insulating material for electronic circuit boards ofelectronic devices that utilize high frequency bands.

In PTL 1 there is disclosed a technique of adding a curable monomer orpolymer to PPE to form a curable resin composition. In PTL 2, there isdisclosed a method of chemically modifying PPE and combining the PPEwith triallyl isocyanurate and/or triallyl cyanurate as a curablemonomer to form a curable resin composition. PTLs 3 and 4 disclose PPEresin compositions employing low-molecular-weight PPE. Also, PTLs 5 and6 describe methods using opaque dispersions in which particles of aresin composition comprising a crosslinkable resin such as PPE orstyrene-butadiene copolymer and a crosslinking aid such as triallylisocyanurate (TRIC) are dispersed in a non-chlorine-based organicsolvent at ordinary temperature. PTL 7 describes a resin compositioncomprising low molecular weight PPE and an epoxy resin. PTL 8 describesa method employing a varnish in which PPE particles are dispersed in asolvent consisting of at least 90% water.

PTL 9 describes a low-dielectric resin comprising a PPE-modifiedbutadiene polymer, an inorganic filler and a saturated thermoplasticelastomer. PTL 10 describes a high-frequency multilayer wiring boardemploying PPE as a low-dielectric resin. PTL 11 describes a laminatingmaterial employing a thermosetting resin comprising a resin with apolyphenylene oxide backbone and TAIL, as a low-dielectric resin.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Publication SHO No. 61-287739

PTL 2: Japanese Unexamined Patent Publication HEI No. 4-239017

PTL 3: Japanese Unexamined Patent Publication No. 2002-26577

PTL 4: Japanese Unexamined Patent Publication No. 2008-260942 PTL 5:Japanese Unexamined Patent Publication HEI

No. 7-292126

PTL 6: Japanese Unexamined Patent Publication No. 2008-50528

PTL 7: Japanese Unexamined Patent Publication No. 2006-63114

PTL 8: Japanese Unexamined Patent Publication No. 2003-34731

PTL 9: International Patent Publication No. WO2008/136373

PTL 10: Japanese Unexamined Patent Publication No. 2004-140268

PTL 11: Japanese Unexamined Patent Publication No. 2003-283098

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, the technologies described in PTLs 1 to 8 still have much roomfor improvement from the viewpoint of obtaining prepregs exhibiting theexcellent dielectric characteristics of PPE while having low resin dustfall-off or resin flaking during production and handling, and also withexcellent adhesion of cured products (interlayer peel strength ofmultilayer boards, or peel strength between cured curable resincompositions and metal foils such as copper foils).

On the other hand, while the technologies described in PTLs 9 to 11 aredesigned to improve adhesion between low-dielectric resins and metalfoils, they cannot adequately be applied for reducing roughness andthicknesses of metal foils, and therefore they have also had room forimprovement. Furthermore, the technologies described in PTLs 9 to 11were not developed from the viewpoint of improving resin crackingoccurring near the base material or metal foil under thermal load,moisture absorption load and mechanical load.

In light of this situation, it is an object of the present invention toprovide a prepreg exhibiting the excellent dielectric characteristics ofPPE while also having satisfactory adhesion, and therefore having lowresin dust fall-off or resin flaking during production and handling ofprepregs.

It is another object to provide a laminated sheet that can minimizecracking due to stress acting as a result of thermal load, moistureabsorption load and mechanical load during production and handling.

Means for Solving the Problems

As a result of much diligent research conducted with the aim of solvingthe problems described above, the present inventors have completed thisinvention based on the knowledge of the finding that when a prescribedamount of PPE particles is added to a prepreg and the content ratio,particle size and PPE content of the PPE particles are controlled toprescribed ranges, this improves the adhesion exhibited between a basematerial, and the PPE-containing curable resin of the prepreg or a boardproduced by hot pressure molding from the prepreg.

The present inventors further found that in a layered material composedof a low-dielectric resin, a base material and a low-roughness metalfoil, increasing the metal foil peel strength to above a certain valueand maintaining a suitable range for the coefficient of linear thermalexpansion of the laminated sheet, as well as controlling the ratiobetween the metal foil peel strength and the peel strength between thelow-dielectric resin and the base material to within a prescribed range,inhibits cracking between each of the layers or near the layers,allowing application of low-roughness copper foils, and the inventionhas been completed upon this finding.

Specifically, the present invention is as follows.

[1] A PPE-containing prepreg comprising a base material and a curableresin composition containing polyphenylene ether (PPE) particles,wherein:

(1) PPE extracted from the prepreg using a toluene/methanol mixedsolvent with a mass ratio of 95:5 includes insoluble PPE particles (A)in the mixed solvent,

(2) the content of PPE in the PPE particles (A) is 70 mass % or greater,and

(3) the number-average molecular weight of the PPE in the PPE particles(A) is between 8,000 and 40,000.

[2] A PPE-containing prepreg according to [1] above, wherein at least60% of all of the PPE particles (A) have sizes of between 0.3 μm and 200μm, and at least 60% of all of the PPE particles (A) have sizes ofbetween 1.0 μm and 100 μm.

[3] A PPE-containing prepreg according to [1] or [2] above, wherein atleast 60% of all of the primary particles (A′) composing the PPEparticles (A) have sizes of between 0.3 μm and 30 μm, and at least 60%of all of the particles have particle sizes of between 0.3 μm and 20 μm.

[4] A PPE-containing prepreg according to [3] above, wherein the maximumparticle size of the primary particles (A′) composing the PPE particles(A) is no greater than 40 μm.

[5] A PPE-containing prepreg according to any one of [1] to [4] above,wherein also:

(4) PPE extracted from the prepreg using a toluene/methanol mixedsolvent with a mass ratio of 95:5 includes dissolved PPE (B) which isdissolved in the mixed solvent, in addition to the insoluble PPEparticles (A) in the mixed solvent, and

(5) the mass ratio of the PPE particles (A) and the dissolved PPE (B) is99:1 to 45:55.

[6] A PPE-containing prepreg according to [5] above, wherein thenumber-average molecular weight of the dissolved PPE (B) is between5,000 and 40,000.

[7] A PPE-containing prepreg according to [5] above, wherein thenumber-average molecular weight of the dissolved PPE (B) is between1,000 and 7,000, and the average number of phenolic hydroxyl groups permolecule is less than 0.5.

[8] A PPE-containing prepreg according to any one of [1] to [7] above,wherein the content of PPE in the curable resin composition is between10 mass % and 70 mass % based on 100 mass % as the curable resincomposition.

[9] A PPE-containing prepreg according to any one of [1] to [8] above,further comprising a crosslinking curable component (C) and an initiator(D).

[10] A PPE-containing prepreg according to [9] above, wherein thecrosslinking curable component (C) is a monomer with two or more vinylgroups in the molecule.

[11] A PPE-containing prepreg according to [10] above, wherein thecrosslinking curable component (C) is triallyl isocyanurate (TRIC).

[12] A PPE-containing prepreg according to any one of [1] to [11],further comprising an epoxy resin at a content of between 0.1 mass % and10 mass %. [13] An electronic circuit board formed using aPPE-containing prepreg according to any one of [1] to [12], or itsmaterial.

[14] A laminated sheet comprising a low-dielectric resin and a basematerial, wherein:

(1) the dielectric loss tangent of the laminated sheet at 10 GHz is nogreater than 0.007 (cavity resonance method),

(2) the metal foil peel strength of the laminated sheet with a metalfoil that has a side with a surface smoothness of no greater than Rz 2.0μm is 0.6 N/mm or greater,

(3) the coefficient of linear thermal expansion of the laminated sheet(≦Tg) is between 20 ppm/K and 60 ppm/K, and

(4) the peel strength between the low-dielectric resin and the basematerial is between 0.8 and 1.8 times the metal foil peel strength.

[15] A laminated sheet according to [14] above, wherein the Tg of thelaminated sheet is 180° C. or higher.

[16] A laminated sheet according to [14] or [15] above, wherein thethickness of the metal foil is less than 35 μm.

[17] A laminated sheet according to any one of [14] to [16] above,wherein the metal foil peel strength of the laminated sheet with a metalfoil that has a side with a surface smoothness of no greater than Rz 2.0μm is 0.8 N/mm or greater.

[18] A laminated sheet according to any one of [14] to [17] above,wherein the peel strength of the laminated sheet with the low-dielectricresin and the base material is 0.6 N/mm or greater.

[19] A laminated sheet according to any one of [14] to [18] above,wherein the ratio between the peel strength of the laminated sheet withthe low-dielectric resin and the base material, and the metal foil peelstrength (base material-resin/metal foil ratio) is between 1.05 and 1.8.

[20] A laminated sheet according to [19] above, wherein the ratiobetween the peel strength of the laminated sheet with the low-dielectricresin and the base material, and the metal foil peel strength (basematerial-resin/metal foil ratio) is between 1.3 and 1.8.

[21] A laminated sheet according to any one of [14] to [20] above,wherein the low-dielectric resin comprises polyphenylene ether (PPE) atbetween 10 mass % and 70 mass % based on 100 mass % as thelow-dielectric resin.

[22] A laminated sheet according to any one of [14] to [21] above,formed using a PPE-containing prepreg according to any one of [1] to[12].

[23] A laminated sheet according to [21] or [22] above, wherein the PPEhas a number-average molecular weight of between 1,000 and 7,000, andthe average number of phenolic hydroxyl groups per PPE molecule isbetween 0.1 and 0.6.

Effect of the Invention

According to the invention there is provided a prepreg exhibiting theexcellent dielectric characteristics of PPE while also havingsatisfactory adhesion, and therefore having low resin dust fall-off orresin flaking during production and handling of prepregs. There isfurther provided a laminated sheet that can minimize cracking due tostress acting as a result of thermal load, moisture absorption load andmechanical load during production and handling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a carbon nuclear magnetic resonance spectrum of an extract(A) obtained by the method of Example 1, and a carbon nuclear magneticresonance spectrum of a standard substance.

FIG. 2 is a photographic image of a prepreg with PPE particles (Example2) and a prepreg without PPE particles (Comparative Example 1), after apowder fall-off and peeling test.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detail,with the understanding that the invention is not to be limited thereto.The first embodiment is a prepreg constructed from a base material and acurable resin composition containing PPE particles.

<Polyphenylene Ether (PPE)>

According to the first embodiment, the PPE preferably includes arepeating structural unit represented by the following formula (1):

[wherein R1, R2, R3 and R4 each independently represent hydrogen, ahalogen atom, or optionally substituted alkyl, optionally substitutedalkoxy, optionally substituted aryl, optionally substituted amino group,nitro group or carboxyl].

Specific examples for PPE include poly(2,6-dimethyl-1,4-phenyleneether), poly(2-methyl-6-ethyl-1,4-phenylene ether),poly(2-methyl-6-phenyl-1,4-phenylene ether),poly(2,6-dichloro-1,4-phenylene ether) and the like, as well ascopolymers of 2,6-dimethylphenol with other phenols (for example,2,3,6-trimethylphenol or 2-methyl-6-butylphenol), and polyphenyleneether copolymers obtained by coupling of 2,6-dimethylphenol withbiphenols or bisphenols, among which a preferred example ispoly(2,6-dimethyl-1,4-phenylene ether).

Throughout the present specification, “PPE” refers to a polymercomprising a substituted or unsubstituted phenylene ether unitstructure, and it may include another copolymerizing component.

The prepreg of the first embodiment contains insoluble PPE particles (A)in a toluene/methanol mixed solvent with a mass ratio of 95:5, as PPEextracted from the mixed solvent.

If such PPE particles (A) are present in the prepreg, it is possible toinhibit film formation by the resin layer during the step of drying thesolvent after the resin varnish has been coated during production of theprepreg. This is preferred to help prevent formation of a film-likesubstance on the surface layer of the complex of the curable resincomposition and the base material, and peeling off of the film-likesubstance during the subsequent prepreg production process and handling.It is also preferred because, for the same reason, it can inhibitformation of a film-like substance on the surface layer of the complexof the curable resin composition and the base material during the stepof coating the resin varnish during production of the prepreg, thuseliminating escape channels for the gasified solvent from the interiorof the complex and consequently minimizing the phenomenon of residualvoids between the base material and the resin layer. For reference, FIG.2 shows a photographic image of a prepreg with PPE particles (Example 2)and a prepreg without PPE particles (Comparative Example 1), after apowder fall-off and peeling test. Also, inhibiting film formation of theresin layer reduces the solvent drying load during the drying step, andis therefore preferred from the viewpoint of minimizing ongoingdeterioration caused by residual solvent and inhibition of curing of thecurable resin composition.

Furthermore, the presence of such PPE particles (A) in the prepreg canimprove adhesion between the base material and the cured resin andadhesion between the cured resin and the metal foil. This is preferredbecause it will increase the interlayer peel strength and copper foilpeel strength of the cured complex, and will also tend to provide thecured complex with increased moisture absorption resistance, heatresistance, and stability of electrical characteristics underhygroscopic conditions.

While the reason is not fully understood, it is believed that underordinary hot pressure molding conditions, this allows the melting rateof the PPE particles (A) to be appropriately delayed with respect tothat of the thermosetting resin components other than the PPE particles(A). As a result, the thermosetting resin components other than the PPEparticles (A) fuse first and cover the surface of the base material andstrongly adhere to the base material. In addition, it is conjecturedthat since the molten PPE component becomes covered with a delay afterthe PPE particles (A) and the thermosetting resin cures during theprocess of compatibilization between the thermosetting resin componentsand the PPE component, adhesion between the base material and the curedcurable resin composition is satisfactory. A preferred form for the PPEparticles (A) for achieving satisfactory adhesion between the basematerial and the cured curable resin composition will be describedbelow.

The PPE particles (A) contain PPE at 70 mass % or greater, preferably 80mass % or greater, more preferably 85 mass % or greater and even morepreferably 90 mass % or greater.

If the PPE component in the PPE particles (A) is present within thisrange, adhesion between the base material and the cured thermosettingresin composition in the cured complex described below will besatisfactory, and this will tend to yield a cured complex havingmoisture absorption resistance, heat resistance and excellent electricalcharacteristics under hygroscopic conditions.

The reason for this is not entirely clear, but the followingexplanations are possible.

(i) The high PPE content of the PPE particles (A) results in a low PPEcomponent content in the components other than the PPE particles,thereby increasing the content of the thermosetting resin componentsother than the PPE component.

(ii) The PPE particles (A) have a slower melting rate than thethermosetting resin components other than the PPE particles (A).

(iii) During the hot pressure molding process, first the thermosettingresin components other than the PPE particles (A), which have a rapidmelting rate, undergo melting and cover the surface of the basematerial. During this time, adhesion with the base material is strongerbecause of the large content ratio of the thermosetting resin componentsother than the PPE component.

(iv) Next, presumably the molten PPE component becomes covered with adelay after the PPE particles (A) and the thermosetting resin curesduring the process of compatibilization between the thermosetting resincomponents and the PPE component, so that adhesion between the basematerial and the cured curable resin composition is satisfactory.

The number-average molecular weight of the PPE in the PPE particles (A)is between 8,000 and 40,000. The preferred range for the number-averagemolecular weight is between 8,500 and 30,000, and a more preferred rangeis between 9,000 and 25,000.

A number-average molecular weight of 8,000 or greater is preferred sincethis will tend to provide satisfactory dielectric characteristics, waterabsorption resistance, soldering heat resistance and adhesion (forexample, interlayer peel strength in multilayer boards, or peel strengthbetween copper foils and the cured curable resin composition) for thecured product, which are desirable for high-frequency electronic circuitboards. The number-average molecular weight of the PPE in the PPEparticles (A) is also preferably no greater than 40,000 because thiswill tend to lower the melt viscosity of the curable resin compositionduring molding and result in satisfactory moldability.

The percentage of the number of particles with long diameters of between0.3 μm and 200 μm with respect to the total number of the PPE particles(A) is preferably 60% or greater, also preferably 70% or greater,preferably 80% or greater, preferably 90% or greater, preferably 95% orgreater and preferably 98% or greater. The upper limit is preferably nogreater than 100%.

The percentage of the number of particles with long diameters of between1.0 μm and 100 μm with respect to the total number of the PPE particles(A) is preferably 60% or greater, also preferably 70% or greater,preferably 80% or greater, preferably 90% or greater, preferably 95% orgreater and preferably 98% or greater. The upper limit is preferably nogreater than 100%.

The percentage of the number of particles with long diameters of between3 μm and 20 μm with respect to the total number of the PPE particles (A)is preferably 60% or greater, also preferably 70% or greater, preferably80% or greater, preferably 90% or greater, preferably 95% or greater andpreferably 98% or greater. The upper limit is preferably no greater than100%.

The percentage of the number of particles with long diameters of between0.3 μm and 30 μm with respect to the total number of the PPE particles(A) is preferably 60% or greater, also preferably 70% or greater,preferably 80% or greater, preferably 90% or greater, preferably 95% orgreater and preferably 98% or greater. The upper limit is preferably nogreater than 100%.

The percentage of the number of particles with long diameters of between0.3 μm and 20 μm with respect to the total number of the PPE particles(A) is preferably 60% or greater, also preferably 70% or greater,preferably 80% or greater, preferably 90% or greater, preferably 95% orgreater and preferably 98% or greater. The upper limit is preferably nogreater than 100%.

The percentage of the number of particles with long diameters of between0.3 μm and 3 μm with respect to the total number of the PPE particles(A) is preferably 60% or greater, also preferably 70% or greater,preferably 80% or greater, preferably 90% or greater, preferably 95% orgreater and preferably 98% or greater. The upper limit is preferably nogreater than 100%.

It is conjectured that, among these ranges, if at least 80% of the totalnumber of PPE particles have sizes of 0.3 μm or greater and at least 60%of the total number of PPE particles have sizes of 1.0 μm or greater,then this allows the melting rate of the PPE particles during hotpressure molding to be appropriately slower compared to thethermosetting resin composition other than the PPE particles, but it ispreferred for satisfactory adhesion between the base material and thecured curable resin composition of the cured complex described below.

Another presumed reason is that if at least 80% of the total number ofPPE particles have sizes of no greater than 200 μm and at least 60% ofthe total number of PPE particles have sizes of up to 100 μm, the PPEcomponent in the PPE particles completely melts under ordinary hotpressing conditions, and this is preferred because it allows the curableresin component to sufficiently fill the voids of the base material (forexample, between filaments of a filamentous substrate such as a glasscloth), and the irregularities in the wiring. Sufficient melting of thePPE component in the PPE particles is preferred from the viewpoint ofinhibiting molding defects such as voids and thin spots.

According to the first embodiment, the PPE particles (A) extracted fromthe prepreg with a toluene/methanol mixed solvent at a mass ratio of95:5 are preferably composed of primary particles (A′). In the primaryparticles (A′),

the percentage of the number of particles with long diameters of between0.3 μm and 200 μm among the total number of particles,

the percentage of the number of particles with long diameters of between1.0 μm and 100 μm among the total number of particles,

the percentage of the number of particles with long diameters of between3 μm and 20 μm among the total number of particles,

the percentage of the number of particles with long diameters of between0.3 μm and 30 μm among the total number of particles,

the percentage of the number of particles with long diameters of between0.3 μm and 20 μm among the total number of particles, and

the percentage of the number of particles with long diameters of between0.3 μm and 3 μm among the total number of particles,

are preferably in the same percentage ranges as for the PPE particles(A).

It is conjectured that, among these ranges, if at least 80% of the totalnumber of PPE primary particles have sizes of between 0.3 μm and 30 μm,and at least 60% of the total number of PPE primary particles have sizesof between 0.3 μm and 20 μm, then this allows the melting rate of thePPE particles during hot pressure molding to be appropriately slowercompared to the thermosetting resin composition other than the PPEparticles, but it is preferred for satisfactory adhesion between thebase material and the cured curable resin composition of the curedcomplex described below.

Also, presumably if at least 80% of the PPE primary particles have sizesof no greater than 30 μm and at least 60% of the PPE primary particleshave sizes of up to 20 μm, then it will be possible to rapidly limit themelting rate of the PPE component in the PPE particles (A) to within asuitable range, thereby allowing uniform compatibilization between thePPE component that has melted with a delay compared to the PPE particles(A), and the thermosetting resin components other than the PPE particles(A), and contributing to improved adhesion.

In addition, preferably at least 60% of the PPE primary particles havesizes of between 0.3 μm and 3 μm, since this will result in excellentstability of the electrical characteristics of the cured complexdescribed below, under hygroscopic conditions. While the reason for thisis not completely understood, it is possibly due to the fact that thedifference between the melting rate of the PPE particles and the meltingrate of the thermosetting resin composition other than the PPE particlesduring hot pressure molding is optimal for satisfactory impregnation ofthe curable resin composition into the base material and adhesionbetween the curable resin composition and the base material, and thatmoisture absorption into the boundary region between the curable resincomposition and the base material is minimized.

The maximum diameter of the PPE particles (A) or primary particles (A′)is preferably no greater than 40 μm, more preferably no greater than 30μm, even more preferably no greater than 20 μm and most preferably nogreater than 8 μm. The lower limit is preferably at least 0.5 μm.

This is presumably because if the maximum diameter is no greater than 40μm, the PPE component in the PPE primary particles completely meltsunder ordinary hot pressing conditions, and this is preferred because itallows the curable resin component to sufficiently fill the voids of thebase material (for example, between filaments of a filamentous substratesuch as a glass cloth), and the irregularities in the wiring. Sufficientmelting of the PPE component in the PPE particles is preferred from theviewpoint of inhibiting molding defects such as voids and thin spots.

The lower limit for the maximum diameter is preferably at least 0.5 μmfrom the viewpoint of more satisfactorily exhibiting an excellent effectof adhesion between the base material and the cured curable resincomposition.

According to the first embodiment, PPE extracted from the prepreg with atoluene/methanol mixed solvent at a mass ratio of 95:5 preferably alsocontains dissolved PPE (B), which is soluble in the mixed solvent, inaddition to the PPE particles (A) that are insoluble in the mixedsolvent.

Also, the mixing ratio of the PPE particles (A) and the dissolved PPE(B) is preferably 99:1 to 45:55, more preferably 99:1 to 60:40, evenmore preferably 99:1 to 75:25 and most preferably 99:1 to 85:15, as theratio of PPE particles (A):dissolved PPE (B) (mass ratio).

Preferably, the mass ratio is the same as 99:1 or the proportion of PPEparticles (A) is lower, from the viewpoint of reducing resin dustfall-off or resin flaking that occurs during production of the prepregor during handling of the prepreg. This is believed to be because thethermosetting resin component containing the dissolved PPE (B) liesbetween the base material and the PPE particles (A).

On the other hand, preferably the mass ratio is 45:55 or the proportionof PPE particles (A) is higher, for satisfactory adhesion between thebase material and the cured thermosetting resin composition of the curedcomplex described below. While the reason for this is not completelyunderstood, it is possible that, as mentioned above, the thermosettingresin component containing the dissolved PPE particles (B) other thanthe PPE particles (A) melts first during the prepreg hot pressuremolding process, thereby covering the surface of the base material andadhering to the base material, but since the amount of the PPE componentin the thermosetting resin component at this time can be reduced,adhesion with the base material is reinforced.

Also, the number-average molecular weight of the dissolved PPE (B) ispreferably 5,000 to 40,000. A more preferred range for thenumber-average molecular weight of the dissolved PPE (B) is between5,500 and 30,000, and an even more preferred range is between 6,000 and25,000.

The number-average molecular weight of the dissolved PPE (B) ispreferably 5,000 or greater for satisfactory electrical characteristicsof printed circuit boards produced using the dispersion. Thenumber-average molecular weight of the dissolved PPE (B) is preferablyno greater than 40,000 from the viewpoint of obtaining low meltviscosity for the curable resin composition and satisfactorymoldability, during molding of the prepreg obtained by impregnating abase material with a varnish containing the PPE particle dispersion.

In the dissolved PPE (B), the number-average molecular weight ispreferably between 1,000 and 7,000 and the average number of phenolichydroxyl groups per molecule is preferably no greater than 0.5.

A more preferred range for the number-average molecular weight of thedissolved PPE (B) is between 1,300 and 5,000, and an even more preferredrange is between 1,500 and 4,000. The number-average molecular weight ofthe dissolved PPE (B) preferably no greater than 7,000 because this willtend to lower the melt viscosity of the curable resin composition andresult in satisfactory moldability during hot pressure molding. On theother hand, a number-average molecular weight of 1,000 or greater ispreferred since this will tend to allow maintenance of satisfactorydielectric characteristics, water absorption resistance, soldering heatresistance and adhesion (for example, interlayer peel strength inmultilayer boards, or peel strength between copper foils and the curedcurable resin composition) for the cured product, which are desirablefor high-frequency electronic circuit boards.

According to the first embodiment, the PPE component in the prepreg ispreferably between 10 mass % and 70 mass % based on 100 mass % as themass of the curable resin composition in the prepreg. The preferredrange for the percentage of the PPE component in the curable resincomposition is between 13 mass % and 60 mass %, and an even morepreferred range is between 15 mass % and 50 mass %.

The percentage of the PPE component among the curable resin componentsin the prepreg is the value determined by the following method.

First, the amount of the curable resin composition in the prepreg isdetermined by the following method. A 50 g portion of chloroform at 23°C.±2° C. is added to 2.5 g of the prepreg. After allowing 1 hour to passin a thermostatic chamber at 23° C.±2° C. while vigorously shaking every5 minutes, the curable resin composition dissolved in the chloroform isrecovered by filtration. Next, 50 g of chloroform at 23° C.±2° C. isadded to the extraction residue, and after 1 hour in a thermostaticchamber at 23° C.±2° C. while vigorously shaking every 5 minutes in thesame manner, the curable resin composition dissolved in the chloroformis recovered by filtration. The two recovered chloroform solutionbatches are combined and the solvent is removed to obtain a curableresin composition, and the weight is measured as the mass of the curableresin composition in 2.5 g of prepreg.

Also, the amount of PPE component in the prepreg is calculated as thesum of the mass of PPE component in the PPE particles (A), calculatedfrom the mass of the PPE particles (A) in 2.5 g of prepreg and the PPEcontent of the PPE particles (A), and the mass of the dissolved PPE (B)in 2.5 g of prepreg, determined by the method described below.

The mass ratio of the PPE component with respect to the curable resincomposition is calculated from the mass of the curable resin compositionand the mass of the PPE component in 2.5 g of prepreg, obtained by themethod described above.

The percentage of the PPE component in the resin composition ispreferably at least 10 mass %, because the PPE content will increase inthe printed circuit board obtained by hot pressure molding of theprepreg and a printed circuit board with excellent electricalcharacteristics will be obtained. The percentage of PPE component in theresin composition is preferably no greater than 70%, because this willprevent excessive increase in the melt viscosity of the PPEparticle-containing prepreg during the hot pressure molding process anda homogeneous, satisfactory molded article will be obtained.

There is no particular restriction on the average number of phenolichydroxyl groups per PPE molecule in the PPE of first embodiment.

For example, the average number of phenolic hydroxyl groups per PPEmolecule may be set to be less than 0.5. It is more preferably nogreater than 0.2 and even more preferably no greater than 0.1. Theaverage number of phenolic hydroxyl groups is preferably less than 0.5,because this will allow formation of a cured product with lowpermittivity and a low dielectric loss tangent even when using PPE ofrelatively low molecular weight. It is also preferred because it willminimize curing inhibition by phenolic hydroxyl groups, so as to obtaina cured product with satisfactory curing reactivity and with excellentmechanical properties and heat resistance. A low average number ofphenolic hydroxyl groups is preferred, and it may even be zero, but thelower limit will generally be about 0.001 from the viewpoint of allowingmodification of phenolic hydroxyl groups with other functional groups.

The average number of phenolic hydroxyl groups per PPE molecule may alsobe set to be 0.3 or greater. It is preferably 0.7 or greater, morepreferably 0.9 or greater and even more preferably 1.05 or greater. Byusing PPE with an average number of phenolic hydroxyl groups of 0.3 orgreater per molecule in the curable resin composition, the adhesionbetween the cured resin composition and the base material (for example,a glass cloth) or the adhesion between the cured resin composition and ametal foil such as a copper foil will be satisfactory, and waterabsorption resistance and soldering heat resistance of the printedcircuit board and the adhesion (for example, the interlayer peelstrength for a multilayer board, or the peel strength between the curedproduct and the copper foil) will be even more satisfactory, and this istherefore preferred. The average number of phenolic hydroxyl groups ispreferably no greater than 2.0, more preferably no greater than 1.85 andeven more preferably no greater than 1.6, from the viewpoint ofminimizing increase in the water absorbing property of the complexcomprising the cured curable resin composition and the base material(for example, a laminated sheet) or from the viewpoint of minimizingincrease in the permittivity and dielectric loss tangent of the complex.

The average number of phenolic hydroxyl groups per PPE molecule can beadjusted, for example, by mixing PPE having residual molecular terminalphenolic hydroxyl groups and PPE having molecular terminal phenolichydroxyl groups modified with other functional groups, and adjustingtheir mixing ratio. Alternatively, it can be adjusted by changing thedegree of substitution of the molecular terminal phenolic hydroxylgroups with other functional groups. The types of such functional groupsare not particularly restricted, and they may be benzyl, allyl,propargyl, glycidyl, vinylbenzyl, methacryl or the like. Among these,the functional groups are preferably benzyl groups from the viewpoint ofsatisfactory reaction efficiency, ready commercial availability, lowinherent reactivity and excellent stability, and obtaining a notableeffect of reducing the melt viscosity of the PPE-containing compositionduring press molding. Alternatively, there may be suitably used allyl,propargyl, glycidyl, vinylbenzyl or methacryl groups, from the viewpointof allowing formation of crosslinking reaction during the hot pressuremolding process and obtaining a cured product with excellent mechanicalproperties and heat resistance.

<Other Components>

The curable resin composition preferably contains a crosslinking curablecomponent (C) in addition to the aforementioned PPE.

The crosslinking curable component (C) is preferably a monomer havingtwo or more unsaturated groups in the molecule. The resin dispersion maycontain the crosslinking curable component (C) at preferably 5 to 95parts by weight, more preferably 10 to 80 parts by weight, even morepreferably 10 to 70 parts by weight and most preferably 20 to 70 partsby weight, with respect to 100 parts by weight of the PPE (A). If theamount of the crosslinking curable component (C) is at least 5 parts byweight, it will be possible to satisfactorily reduce the melt viscosityof the resin composition, resulting in satisfactory moldability by hotpressure molding and the like, and to increase the heat resistance ofthe resin composition. On the other hand, if the amount of thecrosslinking curable component (C) is no greater than 95 parts byweight, it will be possible to exhibit the excellent permittivity anddielectric loss tangent of PPE.

Monomers having two or more unsaturated groups in the molecule includetriallyl isocyanurate (TAIL), triallyl cyanurate (TAO), trimethallylcyanurate, trimethylolpropane trimethacrylate, divinylbenzene,divinylnaphthalene, diallyl phthalate, diallyl cyanurate and the like,among which TAIL is preferred for satisfactory compatibility with PPE.

The curable resin composition preferably further contains an initiator(D) for the crosslinking curable component (C).

The initiator (D) used may be any initiator capable of promotingpolymerization reaction of vinyl monomers, and examples includeperoxides such as benzoyl peroxide, cumene hydroperoxide,2,5-dimethylhexane-2,5-dihydroperoxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide,t-butylcumyl peroxide, α,α′-bis(t-butylperoxy-m-isopropyl)benzene,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumyl peroxide, di-t-butylperoxyisophthalate, t-butyl peroxybenzoate,2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane,2,5-dimethyl-2,5-di(benzoylperoxy)hexane, di(trimethylsilyl)peroxide andtrimethylsilyltriphenylsilyl peroxide. Radical generators such as2,3-dimethyl-2,3-diphenylbutane may also be used as reaction initiators.Preferred among these are 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,α,α′-bis(t-butylperoxy-m-isopropyl)benzene and2,5-dimethyl-2,5-di(t-butylperoxy)hexane, from the viewpoint ofobtaining a cured product with excellent heat resistance and mechanicalproperties, low permittivity and a low dielectric loss tangent.

The amount of initiator (D) used may be set as appropriate, butgenerally it is preferably 1.0 part by weight or greater, morepreferably 3.0 parts by weight or greater and even more preferably 5.0parts by weight or greater with respect to 100 parts by weight of thecrosslinking curable component (C) from the viewpoint of satisfactorilypromoting the polymerization reaction, while from the viewpoint ofmaintaining low permittivity and a low dielectric loss tangent for thecured product, it is preferably no greater than 25 parts by weight, morepreferably no greater than 20 parts by weight and even more preferablyno greater than 10 parts by weight.

The curable resin composition may also contain another resin differentfrom PPE (A) (for example, a thermoplastic resin or curable resin).

Examples of thermoplastic resins include homopolymers of vinyl compoundssuch as ethylene, propylene, butadiene, isoprene, styrene,divinylbenzene, methacrylic acid, acrylic acid, methacrylic acid ester,acrylic acid ester, vinyl chloride, acrylonitrile, maleic anhydride,vinyl acetate and ethylene tetrafluoride, and copolymers of two or moreof these vinyl compounds, as well as polyamides, polyimides,polycarbonates, polyesters, polyacetals, polyphenylene sulfides,polyethylene glycols and the like. Preferred for use among these arestyrene homopolymers, styrene-butadiene copolymer andstyrene-ethylene-butadiene copolymer, from the viewpoint of solubilityand moldability in the solvent of the resin composition.

Examples of curable resins include phenol resins, epoxy resins andcyanate esters. The thermoplastic resin and curable resin may also bemodified with a functional compound such as an acid anhydride, epoxycompound, amine or the like.

The amount of such other resins to be used is preferably 10 parts byweight or greater, more preferably 15 parts by weight or greater andeven more preferably 20 parts by weight or greater with respect to 100parts by weight of the PPE (A), and from the viewpoint of exhibiting theexcellent dielectric characteristics and heat resistance of PPE, it ispreferably no greater than 90 parts by weight, more preferably nogreater than 70 parts by weight and even more preferably no greater than50 parts by weight.

When an epoxy resin is to be used as another resin component, in orderto reflect the excellent dielectric characteristic of PPE in the curableresin composition, the range of the epoxy resin in the curable resincomposition is preferably between 0% and 10%, with the range of between0.1% and 10% being more preferred from the viewpoint of increasingadhesion.

The curable resin composition may further contain appropriate additivesaccording to the purpose. Such additives may include flame retardants,heat stabilizers, antioxidants, UV absorbers, surfactants, lubricants,fillers, polymer additives and the like. It is particularly preferredfor the resin composition to also contain a flame retardant, from theviewpoint of imparting flame retardance in addition to the advantages ofobtaining a printed circuit board with satisfactory moldability, waterabsorption resistance and soldering heat resistance and excellentadhesion (for example, interlayer peel strength in multilayer boards orpeel strength between the cured product and copper foils and the like).

The flame retardant is not particularly restricted so long as it has thefunction of inhibiting combustion mechanisms, and there may be mentionedinorganic flame retardants such as antimony trioxide, aluminumhydroxide, magnesium hydroxide and zinc borate, aromatic brominecompounds such as hexabromobenzene, decabromodiphenylethane,4,4-dibromobiphenyl, ethylene bistetrabromophthalimide, andphosphorus-based flame retardants such as resorcinol bis-diphenylphosphate and resorcinol bis-dixylenyl phosphate.Decabromodiphenylethane is preferred among these from the viewpoint ofmaintaining low permittivity and a low dielectric loss tangent for theobtained cured product.

The amount of flame retardant used will differ depending on the flameretardant used and is not particularly restricted, but from theviewpoint of maintaining flame retardance at a UL standard 94V-0 level,it is preferably 5 parts by weight or greater, more preferably 10 partsby weight or greater and even more preferably 15 parts by weight orgreater with respect to 100 parts by weight as the total of thefunctional group-added PPE (A) and the crosslinking curable component(C). Also, from the viewpoint of maintaining low permittivity and a lowdielectric loss tangent for the obtained cured product, the amount usedis preferably no greater than 50 parts by weight, more preferably nogreater than 45 parts by weight and even more preferably no greater than40 parts by weight.

Other various additives include heat stabilizers, antioxidants, UVabsorbers, surfactants, lubricants, fillers, polymer additives and thelike. The amounts of such additives used may be appropriately set by aperson skilled in the art as desired.

<Prepreg>

The prepreg of the first embodiment is typically a prepreg for anelectronic circuit board. By using each of the aforementionedcomponents, adhesion between the PPE-containing curable resincomposition and the base material will be satisfactory, making itpossible to provide a prepreg for an electronic circuit board that canyield a cured product having low resin dust fall-off and resin flakingduring production and handling, as well as excellent adhesion by hotpressure molding (for example, interlayer peel strength for multilayerboards, or peel strength between cured curable resin compositions andmetal foils such as copper foils), moisture absorption resistance, heatresistance and stability of electrical characteristics under hygroscopicconditions. PPE characteristically has poor adhesion with base materialsand metal foils. Low molecularization of PPE to increase the number ofterminal hydroxyl groups can potentially improve adhesion, but thistends to impair the original excellent electrical characteristics ofPPE. The prepreg of this embodiment can maintain the excellentelectrical characteristics of PPE while increasing adhesion. Using eachof the components mentioned above is preferred, as this will tend toprovide excellent solubility and dispersibility in aromatic organicsolvents at ordinary temperature and satisfactory handleability, as wellas excellent molten resin flow properties.

A typical prepreg can be produced as a complex of a curable resincomposition and a base material, by impregnating a resin varnishcontaining the curable resin composition into the base material and thenvolatilizing the solvent component by hot air drying or the like.

the base material used may be any of various glass cloths such as aroving cloth, cloth, chopped mat or surfacing mat; an asbestos cloth,metal fiber cloth or other synthesis or natural inorganic fiber cloth; awoven fabric or nonwoven fabric obtained from liquid crystal fibers suchas total aromatic polyamide fibers, total aromatic polyester fibers orpolybenzooxazole fibers; a natural fiber cloth such as cotton cloth,hemp cloth or felt; a natural cellulose-based substrate such as a carbonfiber fabric or a fabric obtained from kraft paper, cotton paper,paper-glass composite yarn or the like, or a polytetrafluoroethyleneporous film, either alone or in combinations of two or more.

The proportion of curable resin composition in the prepreg is preferably30 to 80 parts by weight and more preferably 40 to 70 parts by weightwith respect to 100 parts by weight of the total prepreg. If theproportion is at least 30 parts by weight, excellent insulatingreliability will be obtained when the prepreg is used to form anelectronic board, for example, and if it is no greater than 80 parts byweight, the obtained electronic board will have excellent mechanicalproperties such as flexural modulus.

The method used to fabricate the prepreg may be a method of coating thebase material with a varnish in which the PPE particles are dispersed.

There are no particular restrictions on the method of obtaining thevarnish with the PPE particles (A) dispersed therein.

For example, it may be a method in which PPE particles are dispersed inan organic solvent or PPE is pulverized in an organic solvent to form adispersion of PPE particles with a prescribed particle size (hereunderreferred to as “crushing dispersion method”), or a method in which PPEis added to a halogen-free solvent and then heated to dissolve the PPE,and the temperature is then lowered (hereunder referred to as“crystallization method”). The aforementioned method of obtaining avarnish in which the PPE particles (A) are dispersed is preferred sincethe PPE particles are in a stable state, allowing a prepreg to be stablyproduced.

The particle size of the PPE particles (A) in the prepreg, the PPEcontent ratio, the PPE molecular weight and the mass ratio of the PPEparticles (A) and dissolved PPE (B) can be adjusted, for example, bypre-adjusting the PPE particles to be added to the organic solvent, orby varying the crushing power in the organic solvent, in the “crushingdispersion method” described below. Also, in the “crystallizingdispersion method” described below, it can be adjusted by varying thePPE concentration, the PPE molecular weight, the co-presence and amountof other substances, the temperature lowering speed and the stirringpower.

[Crushing Dispersion Method]

The particle size adjusting method may be pulverization or screening ina wet system or dry system. These methods may also be combined.

The solvent used is preferably a mixed solvent of solvent (a) having aPPE solvent retention of at least 1500% and a solvent (b) having a PPEsolvent retention of no greater than 300%, and the mass ratio (a):(b) ispreferably 90:10 to 99.9:0.1. A more preferred range for the mixed massratio (a):(b) of the solvent (a) with a solvent retention of at least1500% and the solvent (b) of no greater than 300% is 93:7 to 99.5:0.5,and an even more preferred range is 94:6 to 99.2:0.8.

Here, the PPE solvent retention refers to the value determined by thefollowing method.

Approximately 80 g of solvent at 23° C.±2° C. is added to PPE, WO(g)(5±0.1 g) and the mixture is stirred for 2 hours or longer with amagnetic stirrer in a thermostatic chamber at 23° C.±2° C., to prepare auniform dispersion. The obtained dispersion is transferred to a 100 cm³precipitation tube, the solvent is added to a total of 100 cm³, and thedispersion is gently stirred to uniformity, after which it is allowed tostand for 24 hours in a thermostatic chamber at 23° C.±2° C.

Next, the supernatant liquid from the upper and lower separated layersis removed, the mass W of the lower layer (the amount of PPE and thesolvent retained by the PPE).

The solvent retention is calculated by the following formula:

Solvent retention (%)=100×(W−WO)/WO

using the mass WO of the obtained PPE and the combined mass W of the PPEand the solvent retained by the PPE.

In cases where the homogeneous solution or dispersion does not separateinto two layers after standing for 24 hours, the solvent retention isconsidered to be ≧1900%.

Preferably, the mixed mass ratio (a):(b) of the solvent (a) with asolvent retention of at least. 1500% and the solvent (b) of no greaterthan 300% is the same as 90:10, or (a) is greater, because the PPE willbe sufficiently swelled even though the solvent retention of the PPEparticles (A) in the PPE dispersion is high and it has dispersionstability. It is also preferred because, since presumably the molecularchains on the PPE particle surfaces are loosened, the adhesion of thePPE particles is increased, and therefore the prepreg fabricated usingthe PPE particle dispersion and the cured product formed by hot pressuremolding of the prepreg have more satisfactory adhesion with the basematerial and the resin component. Preferably, (a):(b) is the same as99.9:0.1 or (a) is smaller, because excessive swelling of the PPEparticles will be inhibited and it will be possible to ensure the flowproperty of the PPE particle dispersion.

A solvent such that the PPE solvent retention is at least 1500% is notparticularly restricted, but an aromatic organic solvent or the like ispreferred for use so that a solvent retention of at least 1500% can beeasily obtained regardless of the type or molecular weight of the PPE.As preferred examples, there may be used benzene, toluene or xylenealone, or mixtures of two or more thereof may be used. A solvent suchthat the PPE solvent retention is no greater than 300% is also notparticularly restricted, but polar solvents such as alcohols and ketonesare preferably used so that a solvent retention of no greater than 300%can be easily obtained regardless of the type or molecular weight of thePPE. As preferred examples there may be used methanol, ethanol,isopropyl alcohol, methyl ethyl ketone or the like alone, or mixtures oftwo or more thereof may be used.

Dispersion in such organic solvents is preferably carried out at atemperature within no more than 10° C. of the coating temperature. Thiscan avoid loss of homogeneity due to increase in deposition of the PPEduring storage periods before coating or during coating, that results inviscosity increase or variation.

The method for crushing the PPE in the organic solvent and preparing avarnish with the PPE dispersed in the organic solvent may be as follows.

There are no particular restrictions on the solvent used, but it ispreferred to use the solvent (a) in which the PPE solvent retention isat least 1500% and the solvent (b) in which the PPE solvent retention isno greater than 300%, at a mixing ratio such that mass ratio (a):(b) is90:10 to 99.9:0.1, in order to maintain the flow properties anddispersion stability of the PPE particles, and obtain a prepreg withexcellent coating properties on the base material and excellent adhesionbetween the base material and the resin composition containing the PPEparticles. The solvent in which the PPE solvent retention is at least1500% may be an aromatic organic solvent such as benzene, toluene orxylene, for example, either used alone or in mixtures of two or more.Also, the solvent in which the PPE solvent retention is no greater than300% may be a ketone such as methyl ethyl ketone or methyl isobutylketone or an alcohol such as methanol, ethanol or butanol, for example,either used alone or in mixtures of two or more. These solvents may beselected for use as appropriate depending on the PPE used.

If the solvent in which the PPE solvent retention is at least 1500% isat or above a certain level, the PPE particles will swell by taking upthe solvent into the particles, thereby increasing the viscosity,increasing the dispersion stability and allowing a greater coatingamount (resin content) on the base material. It also equalizes the resincomponent dissolved in the solvent and the resin component in theswelled PPE particles, and stabilizes impregnation into the basematerial to allow uniform coating. If the swelling property isinsufficient, the PPE particles become filtered through the basematerial/glass cloth/woven fabric structure at the varnish-impregnatedsections, thereby accumulating on the impregnation roll. On the otherhand, if the solvent in which the PPE solvent retention is at least1500% is limited to no greater than a certain level, this will minimizegelling and solidification of the PPE particles by swelling and allowcoating, while also minimizing progressive swelling and gelling andresulting in excellent storage stability.

[Crystallizing Dispersion Method]

For a method of obtaining PPE crystal grains by adding PPE to ahalogen-free solvent, heating the mixture to dissolution and thenlowering the temperature, particles may be obtained using a PPE solutioncontaining PPE at a solid content of 70 mass % or greater, and loweringthe temperature. Preferably, the content of particles with longdiameters of between 3 μm and 20 μm is at least 60% from the viewpointof obtaining suitable viscosity for coating. Also, preferably the longdiameter/short diameter ratio of the particles is in a range of between1.0 and 1.2 from the viewpoint of obtaining suitable viscosity forcoating, and also from the viewpoint of easily obtaining flow propertiesand increasing the PPE particle concentration of the varnish.

In addition, a higher proportion of PPE in the PPE solution with respectto the dissolved components is preferred from the viewpoint of allowingthe PPE concentration of the PPE particles to be increased and moreeasily obtaining PPE particles according to the first embodiment. ThePPE solution may further contain, in addition to PPE, an additive suchas a polystyrene resin or a hydrogenated block copolymer obtained byhydrogenation of a block copolymer comprising a polymer block A composedmainly of one type of vinyl aromatic compound and a polymer block Bcomposed mainly of at least one type of conjugated diene compound. Also,the PPE solution may contain a component with a melting point of 30° C.or higher, to obtain a PPE crystal solution with flow properties in astable reproducible manner.

The temperature lowering is preferably carried out in a vessel providedwith a stirring blade. The temperature is lowered which stirring the PPEdissolved in a halogen-free solvent, to produce a PPE particledispersion. It is preferred for the stirring to be at a blade tip speedof no greater than 3 m/s when the temperature reaches at least 10° C.higher than the temperature at which the PPE crystal grains begin to bedeposited, in order to prevent particle aggregation and viscosityincrease of the dispersion. Also, the temperature lowering may beconducted in a stationary state from the viewpoint of more easilycontrolling the obtained PPE particles into large spherical shapes andincreasing the flow properties of the dispersion, or allowing the PPEcontent to be increased.

The target temperature for temperature lowering may be near thetemperature at which the varnish is to be impregnated into the basematerial, and for example, if the coating temperature is represented asα° C., it is preferably a temperature of between α−15° C. and α+10° C.,in order to more easily control the mass ratio of the PPE particles (A)and dissolved PPE (B) and obtain a stabilized prepreg. A more preferredrange for the target temperature for temperature lowering is betweenα−10° C. and α+5° C., a more preferred temperature range is between α−5°C. and α+4° C., and the most preferred temperature range is between α−3°C. and α+3° C.

The temperature condition for forming a varnish from the resindispersion obtained in this manner is preferably a temperature ofbetween the target temperature for temperature lowering duringpreparation of the resin dispersion, and the coating temperature, inorder to facilitate control of the mass ratio of the PPE particles (A)and dissolved PPE (B), but it is not particularly restricted so long asit is in a range that allows control of the mass ratio of the PPEparticles (A) and dissolved PPE (B).

When a resin varnish is produced by adding other components to the resindispersion, the addition rate for the other components is preferablyaddition at a rate of no greater than 0.6 part by weight per minute,based on 100 parts by weight of the total PPE content in the dispersion,from the viewpoint of preventing aggregation of the resin.

The solvent used in the dispersion preferably has a PPE solubility ofbetween 3 mass % and 20 mass % at a temperature of 25° C. The PPEsolubility at a temperature of 80° C. is more preferably at least 20mass % and even more preferably 30 mass % or greater. So long as the PPEdissolving properties are satisfied there are no particularrestrictions, but the liquid mixture may be of one type or a mixture oftwo or more. Preferred solvents include aromatic organic solvents suchas benzene, toluene and xylene, ketones such as cyclohexanone, methylethyl ketone and methyl isobutyl ketone, and alcohols such as methanol,ethanol and butanol.

<Curable Resin Composition Complex>

The prepreg may be used to form a laminated sheet with a laminated metalfoil. The laminated sheet preferably has the cured complex and metalfoil stacked and bonded, and it can be suitably used as a material foran electronic board. The metal foil used may be an aluminum foil orcopper foil, for example, with a copper foil being preferred for lowelectrical resistance. The cured complex to be combined with the metalfoil may consist of one sheet or several sheets, and the metal foil maybe stacked on one side or both sides of the complex and the laminatedsheet processed, according to the purpose. The method for producing thelaminated sheet may be a method in which, for example, the prepreg andthe metal foil are stacked and then the curable resin composition iscured, to obtain a laminated sheet in which the cured product layeredbody and metal foil are laminated. One particularly preferred use forthe laminated sheet is as an electronic circuit board.

The second embodiment is a laminated sheet composed of a low-dielectricresin and a base material.

According to the second embodiment, the laminated sheet satisfies thefollowing conditions.

(1) The dielectric loss tangent is no greater than 0.007 at 10 GHz(cavity resonance method).

(2) The metal foil peel strength with a metal foil that has a side witha surface smoothness of no greater than Rz 2.0 μm is 0.6 N/mm orgreater.

(3) The coefficient of linear thermal expansion (≦Tg) is between 20ppm/K and 60 ppm/K.

(4) The peel strength between the low-dielectric resin and the basematerial is between 0.8 and 1.8 times the metal foil peel strength.

By being provided with all of the aforementioned properties, anelectronic circuit board in which a circuit is formed by a low-roughnessmetal foil on a board composed of a low-dielectric resin and a basematerial will not have concentration of stress during productionprocessing (for example, drilling and solder reflow) or during handling,thereby making it resistant to cracking near the base material or nearthe conductor. This can reduce dielectric loss and conductor loss in thehigh-frequency range in addition to using a low-roughness metal foil,and can provide an electronic circuit board with excellent transmissioncharacteristics and insulating reliability.

The method for reducing the skin resistance of the conductor (metalwiring or the like) may be a method of lowering the surface roughness ofthe conductor, but since low-dielectric resins generally have lowpolarity and unsatisfactory adhesion with conductors, when the surfaceroughness of the conductor is lowered to reduce the anchor effect,adhesion of the resin with the conductor is further reduced, making itimpossible to ensure the required peel strength between the resin andthe conductor. In addition, since a low-dielectric resin will generallyhave low polarity and a relatively rigid structure, the problem arisesthat the resin itself is relatively fragile, and cohesive fracture tendsto occur by stress acting near the base material or metal foil, due tothermal load, moisture absorption load and mechanical load, such thatcracking tends to occur. Although the technologies described in PTLs 9to 11 are designed to improve adhesion between low-dielectric resins andmetal foils, and it is reported that such improvement is possible, thesehave not been developed from the viewpoint of overcoming detachmentbetween the low-dielectric resin and base material, cracking of theresin near the base material, and cracking of the resin near the metalfoil.

<Laminated Sheet>

In a laminated sheet according to the second embodiment, the dielectricloss tangent at 10 GHz is no greater than 0.007. The preferred range forthe dielectric loss tangent is no greater than 0.006, more preferably nogreater than 0.005 and even more preferably no greater than 0.004.

A smaller dielectric loss tangent is desired for the laminated sheet inorder to minimize dielectric loss, but since a low-dielectric resin haslow polarity and a relatively rigid structure, the resin itself isfragile and it tends to lack adhesion with components such as the fillerin the resin, this tendency being greater with low-dielectric resinshaving lower dielectric loss tangents. Consequently, when a dielectricresin with a low dielectric loss tangent is used to form a laminatedsheet, it is unable to withstand stress concentration near the basematerial and near the metal foil under thermal load, moisture absorptionload and mechanical load during production processing (for example,drilling and solder reflow) and during handling, and it becomesdifficult to minimize cracking.

With the construction described above, overall stress is alleviatedwithout being concentrated near the base material or metal foil, andtherefore even when a low-dielectric resin with a dielectric losstangent of 0.007 or lower is used, it is possible to obtain a highlyreliable laminated sheet that is resistant to cracking under thermalload, moisture absorption load and mechanical load, and this istherefore preferred.

In the laminated sheet described above, the metal foil peel strength ofthe laminated sheet with a metal foil that has a side with a surfacesmoothness of no greater than Rz 2.0 μm is 0.6 N/mm or greater. Apreferred range for the metal foil peel strength is 0.8 N/mm or greater,and a more preferred range is 1.0 N/mm or greater.

If the metal foil peel strength is 0.6 N/mm or greater, adhesion betweenthe low-dielectric resin and the metal foil will be firmly maintained,and this is therefore preferred to help prevent peeling and blisteringof the metal foil under thermal load, moisture absorption load andmechanical load in the production processing steps.

Also, the peel strength between the base material and the low-dielectricresin in the laminated sheet is preferably 0.6 N/mm or greater. A morepreferred range for the peel strength between the base material and thelow-dielectric resin is 0.8 N/mm or greater, a more preferred range is1.0 N/mm or greater and the most preferred range is 1.2 N/mm or greater.

The peel strength between the base material and the low-dielectric resinis preferably at least 0.6 N/mm because this will minimize delaminationbetween the layers during production and handling of the laminatedsheet. Although stronger peel strength between the base material and thelow-dielectric resin is preferred from the viewpoint of preventingdelamination, as mentioned above, it is preferred to adjust the strengthratio with the metal foil peel strength to within the followingspecified range in order to adequately exhibit an effect of minimizingresin cracking.

In a laminated sheet, the ratio between the metal foil peel strength andthe peel strength between the base material and the low-dielectric resin(peel strength between laminated sheet base material and low-dielectricresin/laminated sheet copper foil peel strength) (hereunder referred tosimply as “peel strength ratio”) is between 0.8 and 1.8. A preferredrange for the peel strength ratio is between 1.05 and 1.8, a morepreferred range is between 1.3 and 1.8 and an even more preferred rangeis between 1.3 and 1.6.

The peel strength ratio is preferably within this range to help preventcracking of the resin near the base material or near the metal foilunder thermal load, moisture absorption load and mechanical load duringthe production processing steps. While the reason for this is notcompletely understood, it is conjectured that stress generated due tothermal load, moisture absorption load and mechanical load during theproduction processing steps is not concentrated near the base materialor near the metal foil, and can be diffused across the entire laminatedsheet.

The coefficient of linear thermal expansion (Tg) of the laminated sheetis between 20 ppm/K and 60 ppm/K. A preferred range for the coefficientof linear thermal expansion is between 23 ppm/K and 55 ppm/K, and a morepreferred range is between 25 ppm and 50 ppm/K.

It is conjectured that this is because when the coefficient of linearthermal expansion is at least 20 ppm/K, stress produced near the basematerial and the metal foil under thermal load, moisture absorption loadand mechanical load during the production processing steps isefficiently diffused and concentration of stress is alleviated, and thisis preferred in order to help prevent resin cracking.

It is also conjectured that when the coefficient of linear thermalexpansion is no greater than 60 ppm/K deformation of the low-dielectricresin itself is reduced to a minimum, and this is preferred in order tohelp prevent resin cracking near the base material or near the metalfoil under thermal load, moisture absorption load and mechanical loadduring the production processing steps.

The glass transition temperature (Tg) of the laminated sheet ispreferably 180° C. or higher. A more preferred temperature range for theglass transition temperature is 190° C. or higher, an even morepreferred range is 200° C. or higher, and the most preferred range is210° C. or higher.

It is believed that if the glass transition temperature of the laminatedsheet is 180° C. or higher, it is possible to steadily maintain themechanical strength of the low-dielectric resin even when the laminatedsheet is exposed to high temperature in the production processing steps,and this is preferred in order to help prevent resin cracking.

<Metal Foil>

According to the second embodiment, it is possible to form a metal foillaminated sheet with a metal foil layered on the aforementionedlaminated sheet, for the purpose of circuit formation and the like. Themetal foil laminated sheet preferably has the cured complex and metalfoil stacked and bonded, and it can be suitably used as a material foran electronic board.

The metal foil used may be an aluminum foil or copper foil, for example,with a copper foil being preferred for low electrical resistance. Thelayered body to be combined with the metal foil may consist of one sheetor several sheets, and the metal foil may be stacked on one side or bothsides of the layered body and the metal foil laminated sheet processed,according to the purpose.

The metal foil preferably has low surface roughness from the viewpointof reducing conductor loss. A preferred range for the surface roughnessis a Rz of no greater than 2 μm, a more preferred range is no greaterthan 1.5 μm, an even more preferred range is no greater than 1.0 μm, andthe most preferred range is no greater than 0.5 μm.

Also, the surface of the metal foil may be subjected to surfacetreatment such as silane coupling treatment to increase adhesion withthe low-dielectric resin.

The thickness of the metal foil is preferably less than 35 μm. It isbelieved that if the thickness is less than 35 μm, the metal foil easilyfollows deformation when the low-dielectric resin deforms by stressgenerated due to thermal load, moisture absorption load and mechanicalload during the production processing steps, or by relaxation of stress,such that stress is not easily concentrated between the low-dielectricresin and the metal foil, and this is preferred to help preventinclusion of cracks.

<Low-Dielectric Resin>

The low-dielectric resin according to the second embodiment is notparticularly restricted.

There may be suitably used cyanate resins, polyphenylene ethers,amorphous polyolefins, epoxy resins (preferably low-dielectric epoxyresins modified so as to form crosslinking without generating hydroxylgroups during the crosslinking), liquid crystal polymers, and the like,that have excellent dielectric characteristics. Of these, polyphenyleneether resins are preferred for their excellent dielectriccharacteristics, heat resistance, adhesion, moisture absorptionresistance and workability. For example, a thermosetting resincomposition containing the PPE particles as a constituent of the firstembodiment may be used in the low-dielectric resin for the secondembodiment. Such a thermosetting resin composition has excellentdielectric characteristics and excellent adhesion with base materialsand metal foils, and is therefore suitable for satisfying the propertiesfor the second embodiment.

As another example, in the low-dielectric resin of the second embodimentthere may be used PPE having thermosetting functional groups at themolecular chain ends with a number-average molecular weight of between1,000 and 7,000, and an average number of phenolic hydroxyl groups permolecule of between 0.1 and 0.8. A preferred range for thenumber-average molecular weight is between 1,500 and 5,000, a morepreferred range is between 2,000 and 4,000 and an even more preferredrange is between 2,500 and 3,500. Also, a preferred range for thephenolic hydroxyl groups per molecule is between 0.1 and 0.6, a morepreferred range is between 0.1 and 0.5 and an even more preferred rangeis between 0.1 and 0.4.

The number-average molecular weight of the PPE and the average number ofphenolic hydroxyl groups per molecule are the values described for thefirst embodiment.

Preferably, the number-average molecular weight is 1,000 or greater andthermosetting functional groups are present at the molecular chain ends,because it will be possible to accomplish adequate crosslinking reactionduring the pressing and hot molding process, and to obtain a high glasstransition temperature. Also preferably, the number-average molecularweight is no greater than 7,000, because the melt viscosity will bereduced and excellent moldability will be exhibited during the pressingand hot molding process.

In addition, the average number of phenolic hydroxyl groups per moleculeis preferably at least 0.1 to ensure adhesion with the base material andmetal foil, and preferably no greater than 0.8 for excellent electricalcharacteristics and moisture absorption resistance.

Unless otherwise specified, the measured values for each of theparameters mentioned above were measured by the measuring methods in thefollowing examples.

EXAMPLES

This embodiments will now be described in further detail by examples,with the understanding that the embodiments are not in any wayrestricted by the examples. The physical properties mentioned in theexamples, comparative examples and test examples were measured by thefollowing methods.

(1) PPE Content of PPE Particles (A), and Mass Ratio Between PPEParticles and Dissolved PPE (B). [PPE Content Ratio in PPE Particles(A)]

To 2.5 g of prepreg there was added 20 g of a toluene/methanol mixedsolvent at a mass ratio of 95:5, at 23° C.±3° C. One hour was allowed topass in a thermostatic chamber at 23° C.±2° C. while vigorously shakingevery 5 minutes. The mixture was then allowed to stand for 24 hours inthe same thermostatic chamber. Next, the supernatant liquid was removed,5 g of a toluene/methanol mixed solvent with a mass ratio of 95:5 wasadded and the mixture was vigorously shaken, and it was then allowed tostand for 24 hours in the same thermostatic chamber. The supernatantliquid was then removed. After then drying and removing the solvent, itwas developed in chloroform, and after filtering out and removing theinsoluble portion, the chloroform was removed by drying to obtain anextract (this extract will hereunder be referred to as “extract (A)”).The PPE content of the extract (A) was quantified by carbon nuclearmagnetic resonance spectroscopy, and recorded as the PPE content ratioof the PPE particles (A).

Measurement of the PPE content using carbon nuclear magnetic resonancespectroscopy was carried out by the following method. Tetramethylsilaneis used as the reference for the chemical shift, defining the peak as 0ppm. The peak intensities near 16.8, 114.4, 132.5, 145.4 and 154.7 ppmare totaled as the peak for PPE, and the ratio with the peak intensityof tetramethylsilane is calculated as X. Using the value for thestandard substance as X1 and the value for the extract (A) as X2, thevalue of (X2/X1) P 100 can be calculated to measure the PPE content ofthe extract. The signal deriving from PPE may be at the same position asfor the standard substance, with no limitation to the above. Forquantitation, poly(2,6-dimethyl-1,4-phenylene ether) with anumber-average molecular weight of 15,000 to 25,000 was used as thestandard substance, and the peak intensity ratio obtained from an equalamount of measuring sample was used. S202A Grade by Asahi KaseiChemicals Corp. was used as the poly(2,6-dimethyl-1,4-phenylene ether)with a number-average molecular weight of 15,000 to 25,000.

FIG. 1 shows a carbon nuclear magnetic resonance spectrum for an extract(A) obtained by the method of Example 1, and a carbon nuclear magneticresonance spectrum of a standard substance, for reference. First, thesum of the ratios between the signal strengths of 16.8, 114.4, 132.5,145.4 and 154.7 ppm derived from PPE with respect to the signal strengthfor tetramethylsilane, based on the NMR spectrum for the standardsubstance, was used as the signal strength value (X1) for the standardsubstance. Next, the sum of the ratios of each of the signal strengthsof 16.8, 114.4, 132.5, 145.4 and 154.7 ppm at the same signal positionsas for the standard substance with respect to the signal strength fortetramethylsilane in the NMR spectrum of Example 1 was used as thesignal strength value (X2) for Example 1. Using the values for X1 andX2, the PPE content ratio in the PPE particles (A) was calculated by thefollowing formula:

PPE content ratio in PPE particles=(X2/X1)×100=95%

[Mass of PPE Particles (A) in Prepreg]

The mass of the extract (A) was measured and recorded as the mass of PPEparticles (A) in 2.5 g of prepreg.

[Mass of Dissolved PPE (B) in Prepreg]

All of the supernatant liquids obtained during measurement of the PPEcontent ratio of the PPE particles (A) by the procedure described aboveare recovered. The solvent of the supernatant liquid is removed bydrying, and the mass of curable resin composition that is soluble in thesolvent is measured. Next, the PPE content ratio in the curable resincomposition that is soluble in the solvent is determined by quantitationby nuclear magnetic resonance spectroscopy in the same manner as formeasurement of the PPE content ratio of the PPE particles (A). The massof the dissolved PPE (B) in 2.5 g of prepreg was determined from themass of the curable resin composition that was soluble in the solventand the PPE content ratio of the curable resin composition that wassoluble in the solvent, obtained by the method described above.

The mass ratio of (A) and (B) was determined from the mass of the PPEparticles (A) and the mass of soluble PPE (B) in 2.5 g of prepreg,obtained by the method described above.

(2) Number-Average Molecular Weight of PPE in PPE Particles (A) andNumber-Average Molecular Weight of Dissolved PPE (B). [Number-AverageMolecular Weight of PPE in PPE Particles (A)]

The aforementioned extract (A) is used as the measuring sample. Gelpermeation chromatography (GPC) was performed using Shodex LF-804x2(product of Showa Denko K.K.) as the column, 50° C. chloroform as theeluent and an RI (refractometer) as the detector, and the value measuredbased on standard polystyrene was recorded as the number-averagemolecular weight of PPE in the PPE particles (A), from the relationalexpression between the molecular weight of the standard polystyrenesample and the elution time, measured under the same conditions asabove.

[Number-Average Molecular Weight of Dissolved PPE (B)]

The procedure of extracting PPE from the prepreg was carried out by thesame method as for measurement of the PPE content ratio of the PPEparticles (A) described above, and all of the supernatant liquids wererecovered. The supernatant liquids were separated using silica gelcolumn chromatography, to obtain a separated PPE solution. Next, themolecular weight of the PPE in the separated PPE solution was determinedby measurement in the same manner as for the number-average molecularweight of the PPE component in the PPE particles (A).

(3) Measurement of Proportion of Particles with Specific Particle SizesAmong Total Number of PPE Particles (A) or Primary Particles (A′), andMeasurement of Maximum Diameters

To 2.5 g of prepreg there is added 20 g of a toluene/methanol mixedsolvent at a mass ratio of 95:5, at 23° C.±2° C. One hour is allowed topass in a thermostatic chamber at 23° C.±2° C. while vigorously shakingevery 5 minutes. The mixture is then allowed to stand for 24 hours inthe same thermostatic chamber. Next, the supernatant liquid is removed,5 g of a toluene/methanol mixed solvent with a mass ratio of 95:5 isadded and the mixture is again vigorously shaken, and it is then allowedto stand for 24 hours in the same thermostatic chamber. Next, thesupernatant liquid is removed, and 5 g of a toluene/methanol mixedsolvent with a mass ratio of 95:5 is added. After shaking to a uniformdispersion, the dispersion is removed and added dropwise to a samplestage for SEM-EDX measurement. After volatilizing off the solvent,SEM-EDX observation is conducted, particles with a carbon, oxygen andhydrogen total of 95% or greater are considered to be PPE particles, andthe long diameters of the PPE particles (A) and the long diameters ofthe primary particles (A′) are measured. A straight line is drawnrunning through the particle interior, and the length where the straightline is longest is recorded as the long diameter of the particle. Formeasurement of the long diameters of the PPE particles (A), the longdiameters of 400 or more PPE particles are randomly measured. Formeasurement of the long diameters of the primary particles (A′), thelong diameters of 400 or more PPE primary particles are randomlymeasured.

The number of PPE particles with a specific particle size aredetermined, and the proportion is calculated with respect to the totalnumber of measured particles, and recorded as the proportion ofparticles with the specific particle size among the total number of PPEparticles. The maximum long diameter is the maximum value of the longdiameter among those measured.

(4) Powder Fall-Off and Peeling (180°, 90°) of Prepreg

Resin dust fall-off or resin detachment upon folding the prepreg 180°was examined and evaluated. First, the prepreg was cut to a size of 200mm P 300 mm using a cutter blade. Next, the prepreg was folded 180° withthe two rectangular long sides against each other, and then restored.The prepreg was then folded 180° with the two rectangular short sidesagainst each other, and then restored. Samples without problems such asresin dust fall-off or resin layer peeling in the prepreg handlingprocedure described above were evaluated as “Good” (G). Samples that hadsevere resin dust fall-off were evaluated as “Poor (P)”/resin dustfall-off”, and samples with notable peeling of the resin layer wereevaluated as “Poor (P)/resin peeling”.

A 90° test is the test conducted at 90° instead of 180°. The evaluationmethod is the same as described above.

(5) Average Number of Phenolic Hydroxyl Groups Per PPE Molecule

The number of phenolic hydroxyl groups in the PPE determined from theabsorbance, and the number of PPE molecules determined from the averagemolecular weight, were used to determine the average number of phenolichydroxyl groups per molecule.

First, the number of hydroxyl groups was determined from the valueobtained by measuring the change in absorbance at a wavelength of 318nm, for a sample obtained by adding a tetramethylammonium hydroxidesolution to a methylene chloride solution of the PPE, using anultraviolet and visible absorptiometer, by the method described inJapanese Journal of Polymer Science and Technology, vol. 51, No. 7(1994), p. 480.

Separately, the number-average molecular weight of the PPE wasdetermined by gel permeation chromatography (GPC), and this value wasused to determine the number of PPE molecules. From this value, theaverage number of hydroxyl groups per PPE molecule was calculated by thefollowing formula.

Average number of phenolic hydroxyl groups per PPE molecule=number ofhydroxyl groups/number-average molecular weight

(6) Permittivity and Dielectric Loss Tangent (10 GHz, 1 GHz) ofLaminated Sheet

A laminated sheet was fabricated by stacking and vacuum pressing eightprepregs under conditions with a pressure of 5 kg/cm² while heating fromroom temperature at a temperature-elevating rate of 3° C./rain, and thenwhen a temperature of 130° C. was reached, vacuum pressing underconditions with a pressure of 30 kg/cm² while heating at atemperature-elevating rate of 3° C./rain, and when a temperature of 200°C. was reached, vacuum pressing under conditions with a pressure of 30kg/cm² and a time of 60 minutes while maintaining the temperature of200° C. The laminated sheet was cut to a size of 50 mm P 1.8 mm, as ameasuring sample for permittivity and dielectric loss tangent.

The permittivity and dielectric loss tangent of the laminated sheet at10 GHz were measured under two conditions: steady state and moistureabsorption, by the cavity resonance method using a network analyzer.

The measuring apparatuses used were a network analyzer (N5230A, AgilentTechnologies) and a cavity resonator by Kantoh Electronics Applicationand Development Inc. (Cavity Resonator S Series).

Measurement in the steady state was conducted in an environment at 23°C. and a relative humidity of 65±5%, after placing the measuring samplein an oven at 105° C.±2° C. and drying for 2 hours, and then leaving itin an environment at 23° C. and a relative humidity of 65±5% for 96±5hours.

Also, measurement in the moisture absorption state was conducted in anenvironment at 23° C. and a relative humidity of 65±5%, after placingthe measuring sample in an oven at 105° C. and drying for 2 hours, andthen immersing it in water at 23° C. for 96±5 hours and wiping off thewater on the sample surface.

The permittivity and dielectric loss tangent of the laminated sheet at 1GHz was measured using an impedance analyzer. The measuring apparatusused was an impedance analyzer (4291B op. 002 with 16453A, 16454A,Agilent Technologies), and measurement was conducted with a test stripthickness of approximately 2 mm, a voltage of 100 mV and a frequency of1 MHz-1.8 GHz, determining the average value for 100 sweeps.

(7) Absorption Percentage of Laminated Sheet (Mass %)

A double-sided copper-clad laminate was obtained, by stacking twoprepregs, layering copper foils (thickness: 12 μm, GTS-MP foils,products of Furukawa Electric Co., Ltd.) above and below them, vacuumpressing under conditions with a pressure of 5 kg/cm² while heating fromroom temperature at a temperature-elevating rate of 3° C./rain, and thenwhen a temperature of 130° C. was reached, vacuum pressing underconditions with a pressure of 30 kg/cm² while heating at atemperature-elevating rate of 3° C./min, and when a temperature of 200°C. was reached, vacuum pressing under conditions with a pressure of 30kg/cm² and a time of 60 minutes while maintaining the temperature of200° C. Next, the copper foil was removed by etching to obtain ameasuring sample.

The measuring sample was supplied for a moisture absorption accelerationtest, and the absorption percentage was determined from the increasedmass.

The measuring sample was cut to 50 mm square to prepare a test strip.After drying the test strip at 130° C. for 30 minutes, the mass wasmeasured and recorded as the mass (g) before the acceleration test. Themass was then measured after an acceleration test under conditions witha temperature of 121° C., a pressure of 2 atm and a time of 4 hours, andwas recorded as the mass (g) after the acceleration test.

The mass (g) before the acceleration test and the mass (g) after theacceleration test were used to calculate the absorption percentage bythe following formula, and the mean value for the measured values of 4test strips was determined.

Absorption percentage (mass %)=(Mass before acceleration test−mass afteracceleration test)/mass before acceleration test×100

(8) Soldering Heat Resistance of Laminated Sheet after MoistureAbsorption Test

The measuring sample was used after measurement of the absorptionpercentage described in (7) above, for a solder heat resistance test at288° C. and 260° C. The laminated sheet after the moisture absorptionacceleration test was immersed in a solder bath at 288° C. or 260° C.for 20 seconds, and visually observed. Laminated sheets that were notfound to have blistering, detachment or whitening even when immersed ina solder bath at 288° C. were evaluated as “solder heat-proof 288° C.”.In addition, laminated sheets that exhibited one or more from amongblistering, detachment and whitening after immersion in a solder bath at288° C. but were not found to have blistering, detachment or whiteningeven when immersed in a solder bath at 260° C., were evaluated as“solder heat-proof 260° C.”. Also, laminated sheets that exhibited oneor more from among blistering, detachment and whitening after immersionin a solder bath at 260° C. were evaluated as “poor”.

(9) Copper Foil Peel Strength of Laminated Sheet (Peel Strength N/mm)

A double-sided copper-clad laminate was fabricated, by stacking twoprepregs, layering copper foils (thickness: 35 μm, GTS-MP foils,products of Furukawa Electric Co., Ltd. (evaluation results in Table 1),or thickness: 12 μm, surface roughness Rz: 2.0 μm, FV-WS foil, productsof Furukawa Electric Co., Ltd. (evaluation results in Table 2)) aboveand below them, vacuum pressing under conditions with a pressure of 5kg/cm² while heating from room temperature at a temperature-elevatingrate of 3° C./rain, and then when a temperature of 130° C. was reached,vacuum pressing under conditions with a pressure of 30 kg/cm² whileheating at a temperature-elevating rate of 3° C./min, and when atemperature of 200° C. was reached, vacuum pressing under conditionswith a pressure of 30 kg/cm² and a time of 60 minutes while maintainingthe temperature of 200° C. The double-sided copper-clad laminate wasused as a sample for measurement.

This was based on standard JIS C 6481 for a printed circuit boardcopper-clad laminate test. The measuring sample was cut out to a size of15 mm width P 150 mm length, an autograph (AG-5000D, product of ShimadzuCorp.) was used to measure the mean value of the load when peeling offthe copper foil at an angle of 90° C. with respect to the removal planeat a speed of 50 mm/min, and the mean value for five measurements wascalculated.

(10) Peel Strength (Release Strength) Between Laminated Sheet BaseMaterial and Low-Dielectric Resin

The stress was measured when peeling off one layer of a base materialwith two or more layers composing the laminated sheet at a constantspeed. The double-sided copper-clad laminate fabricated for measurementof the copper foil peel strength of the laminated sheet in (9) (copperfoil: 12 μm thickness, surface roughness Rz=2.0 μm, FV-WS foil, productof Furukawa Electric Co., Ltd.) was used as the measuring sample, thelaminated sheet was cut out to a size of 15 mm width P 150 mm length, anautograph (AG-5000D, product of Shimadzu Corp.) was used to measure themean value of the load when peeling off one layer of the base materialat an angle of 90° with respect to the removal plane at a speed of 50mm/min, and the mean value for five measurements was calculated.

(11) Coefficient of Linear Thermal Expansion of Laminated Sheet (CTE(Ppm/K))

This is the value determined by TMA (Thermo-mechanical analysis), at atemperature of ≦Tg.

The test strip is prepared by removing the metal foil on the surfacelayer by etching and then cutting to 5 mm square. A load of 40 g/cm² isexerted on the test strip, heating is effected at atemperature-elevating rate of 10° C./min, and the change in thickness ofthe test strip is measured. It is then heated from 25° C. to 300° C. Thedegree of change in thickness in the temperature range of 50° C. to 100°C. was divided by the thickness of the test strip, and this valuefurther divided by 50 was recorded as the coefficient of linear thermalexpansion.

(12) Glass Transition Temperature of Cured Product

The dynamic viscoelasticity of the cured test strip was measured and thetemperature of maximum tan δ was determined.

A dynamic viscoelasticity meter (RHEOVIBRON Model DDV-01FP, by Orientec)was used as the measuring apparatus for measurement under the followingconditions: test strip: approximately 35 mm length, approximately 12.5mm width and approximately 0.3 mm thickness, tensile mode, frequency: 10rad/s.

The test strip was prepared by stacking two prepregs, layering 12μm-thick copper foils (GTS-MP foils, products of Furukawa Electric Co.,Ltd.) above and below them, vacuum pressing under conditions with afinal ultimate temperature of 200° C. and a final ultimate pressure of30 kg/cm², to obtain a double-sided copper-clad laminate, and thenremoving the copper foil by etching.

(13) Heat Resistance Test

Eight prepregs were stacked, and copper foils with thicknesses of 12 μmand surface roughnesses Rz of 2.0 μm (FV-WS foils, products of FurukawaElectric Co., Ltd.) were layered on both sides. A copper-clad laminatewas then fabricated by vacuum pressing under conditions with a pressureof 5 kg/cm² while heating from room temperature at atemperature-elevating rate of 3° C./min, and then when a temperature of130° C. was reached, vacuum pressing under conditions with a pressure of30 kg/cm² while heating at a temperature-elevating rate of 3° C./min,and when a temperature of 200° C. was reached, vacuum pressing underconditions with a pressure of 30 kg/cm² and a time of 60 minutes whilemaintaining the temperature of 200° C. One of the copper foils wasremoved by etching, and a heat resistance test was conducted.

The heat resistance test was conducted by a pressure cooker test underconditions of 2 atmospheres, 4 hours, after cutting out the test stripto 50 mm square, placing it in an oven at 105° C. and drying for 2hours. Next, a test of dipping for 20 seconds in a solder bath at 288°C. was repeated 30 times as a heat resistance test. The dipping intervalwas 20 seconds. A cross-section of the sample after heat resistancetesting was observed by SEM.

Production Example 1 Low Molecular Weight Polyphenylene Ether (Mn3,000)>

A 10 L flask was set in an oil bath that had been heated to 90° C., andnitrogen gas was introduced into the flask at 30 ml/min. The procedurewas subsequently carried out under a nitrogen gas stream. After thenadding 1000 g of PPE and 3000 g of toluene, the mixture was stirred todissolution. A solution of 80 g of bisphenol A dissolved in 350 g ofmethanol was then added to the flask while stirring. After continuing tostir for 5 minutes, 3 ml of a mineral spirit solution containing 6 mass% cobalt naphthenate was added through an injector and stirring wascontinued for 5 minutes. Next, 1125 g of toluene was added to 375 g of abenzoyl peroxide solution, and the solution diluted to a benzoylperoxide concentration of 10 mass % was placed in a dropping funnel andadded dropwise to the flask over a period of 2 hours. Upon completion ofthe dropwise addition, heating and stirring were continued for another 2hours to obtain a reaction mixture containing low molecular weight PPE.A large amount of methanol was added thereto to precipitate the lowmolecular weight PPE, and after filtration it was dried to obtain thelow molecular weight PPE. The number-average molecular weight of theobtained low molecular weight PPE was 3,000, and the average number ofphenolic hydroxyl groups per molecule was 1.88.

Production Example 2 Low Molecular Weight/Terminal BenzylatedPolyphenylene Ether (Mn 2,400)>

A 10 L flask was set in an oil bath that had been heated to 90° C., andnitrogen gas was introduced into the flask at 30 ml/min. The procedurewas subsequently carried out under a nitrogen gas stream. After thenadding 1000 g of PPE and 3000 g of toluene, the mixture was stirred todissolution. A solution of 80 g of bisphenol A dissolved in 350 g ofmethanol was then added to the flask while stirring. After continuing tostir for 5 minutes, 3 ml of a mineral spirit solution containing 6 mass% cobalt naphthenate was added through an injector and stirring wascontinued for 5 minutes. Next, 1125 g of toluene was added to 375 g of abenzoyl peroxide solution, and the solution diluted to a benzoylperoxide concentration of 10 mass % was placed in a dropping funnel andadded dropwise to the flask over a period of 2 hours. Upon completion ofthe dropwise addition, heating and stirring were continued for another 2hours to obtain a reaction mixture containing low molecular weight PPE.The number-average molecular weight of the obtained low molecular weightPPE was 2,800, and the average number of phenolic hydroxyl groups permolecule was 1.96.

Next, the temperature of the reaction mixture containing the lowmolecular weight PPE was lowered to 50° C., an aqueous solution of 340 gof sodium hydroxide dissolved in 3050 g of ion-exchanged water, and 31 gof tetrabutylammonium iodide were added, and the mixture was stirred for5 minutes. Next, 1070 g of benzyl chloride was added and the mixture wasstirred at a temperature of 50° C. for 4 hours to obtain a reactionmixture containing low molecular weight/benzylated PPE. The reactionmixture was allowed to stand for separation into two layers, and thelower layer was removed. Water (1000 g) was further added, and afterstirring and standing whereby it again separated into two layers, thelower layer was removed. Next, 200 g of methanol was added, the mixturewas stirred and allowed to stand in the same manner for separation intotwo layers, and the upper layer was removed. There was further added 100g of methanol, the mixture was stirred and allowed to stand in the samemanner for separation into two layers, and then the lower layer wasrecovered to obtain a reaction mixture containing low molecularweight/benzylated. PPE. A large amount of methanol was added thereto toprecipitate the low molecular weight/benzylated PPE, and afterfiltration it was dried to obtain the low molecular weight/benzylatedPPE. The number-average molecular weight of the obtained low molecularweight/benzylated PPE was 3,000, and the average number of phenolichydroxyl groups per molecule was 0.01.

Production Example 3: Low Molecular Weight/Terminal AllylatedPolyphenylene Ether (Mn 2,600)>

Allyl glycidyl ether “NeoallylG” (trademark of Daiso Corp.) (1000 g) washeated to 100° C. and stirred. After thorough mixing, 0.05 g of NaOCH₃was added as a catalyst and the mixture was stirred for approximately 15minutes. It was then heated to 165° C., and a low molecular weight PPEsolution obtained by the same method as Production Example 1 was addedover a period of 90 minutes. During this time, the toluene solvent wasremoved from the reaction system at ordinary pressure or under reducedpressure by streaming nitrogen into the reactor.

The mixture was then stirred at 165° C. for 5 hours and subsequentlyheated to 180° C., and the unreacted allyl glycidyl ether was removedunder reduced pressure to obtain an allylated PPE resin. Thenumber-average molecular weight of the obtained resin was 2900, and theaverage number of phenolic hydroxyl groups per molecule was 0.03.

Production Example 4 Low Molecular Weight/Terminal Partially AllylatedPolyphenylene Ether (Mn 2,600)>

Allyl glycidyl ether “NeoallylG” (trademark of Daiso Corp.) (1000 g) washeated to 100° C. and stirred. After thorough mixing, 0.03 g of NaOCH₃was added as a catalyst and the mixture was stirred for approximately 15minutes. It was then heated to 165° C., and a low molecular weight PPEsolution obtained by the same method as Production Example 1 was addedover a period of 90 minutes. During this time, the toluene solvent wasremoved from the reaction system at ordinary pressure or under reducedpressure by streaming nitrogen into the reactor.

The mixture was then stirred at 165° C. for 5 hours and then heated to180° C., and the unreacted allyl glycidyl ether was removed underreduced pressure to obtain an allylated PPE resin. The number-averagemolecular weight of the obtained resin was 2900, and the average numberof phenolic hydroxyl groups per molecule was 0.43.

Production Example 5 Partially Maleated Polyphenylene Ether (Mn 18,000)>

After dry blending 100 parts by weight of PPE (S202A, product of AsahiKasei Chemicals Corp., number-average molecular weight: 18,000, averagenumber of phenolic hydroxyl groups per molecule: 1.84), 1.5 parts byweight of maleic anhydride and 1.0 part by weight of2,5-dimethyl-2,5-di(t-butylperoxy)hexane (PERHEXA 25B, product of NOFCorp.) at room temperature, it was extruded with a twin-screw extruderunder conditions with a cylinder temperature of 300° C. and a screwrotational speed of 230 rpm, to obtain a reaction product of PPE andmaleic anhydride. The number-average molecular weight of the obtainedreaction product of PPE and maleic anhydride was 17,000, and the averagenumber of phenolic hydroxyl groups per molecule was 0.95.

Example 1

After placing 147 parts by weight of a toluene/methanol mixed solvent(mass ratio: 95:5) in a stainless steel beaker, 32.3 parts of PPE1 and3.6 parts by weight of a styrene-based elastomer were added whilestirring, and stirring was continued for 2 hours. Next, a homomixer(Model HM-300 by As One Corp.) was used for shredding of the PPE underconditions of 25° C., 8,000 rpm for 30 minutes, to obtain a dispersionof PPE particles.

Next, 21.3 parts by weight of triallyl isocyanurate and 2.3 parts byweight of α,α′-bis(t-butylperoxy-m-isopropyl)benzene were added to theobtained PPE dispersion and the mixture was uniformly stirred, afterwhich 15.9 parts of decabromodiphenylethane and 24.6 parts by weight ofsilica were added and the mixture was uniformly stirred to obtain acoating varnish.

The obtained varnish was then impregnated into an E glass cloth with athickness of about 0.1 mm (2116 STYLE, product of Asahi-Schwebel Co.,Ltd.), and after wiping off the excess varnish with a slit, the solventwas removed by drying to obtain a prepreg A with a resin content of 60mass %.

Example 2

After placing 210 parts by weight of a toluene/methanol mixed solvent(mass ratio: 95:5) in a stainless steel beaker, PPE1 and polystyrenewere added in the amounts listed in Table 1 while stirring, and thestirring was continued for 2 hours. Next, a homomixer (Model HM-300 byAs One Corp.) was used for shredding of the PPE under conditions of 25°C., 8,000 rpm for 30 minutes, to obtain a dispersion of PPE particles.

The other curable resin composition components were then added to theobtained PPE dispersion with the formulation listed in Table 1, and themixture was uniformly stirred to obtain a coating varnish.

The obtained varnish was then impregnated into an E glass cloth with athickness of about 0.1 mm (2116 STYLE, product of Asahi-Schwebel Co.,Ltd.), and after wiping off the excess varnish with a slit, the solventwas removed by drying to obtain a prepreg B with a resin content of 60mass %.

Example 3

Prepreg C with a resin content of 60 mass % was obtained by the samemethod as Example 2, except that the amount of toluene was 158 parts byweight.

Examples 4 to 7

Prepregs D to G with resin contents of 60 mass % were obtained by thesame method as Example 2, except for using the formulations listed inTable 1.

Example 8

PPE1 in a methanol solvent was shredded using a homomixer (Model HM-300by As One Corp.) under conditions of 25° C., 8,000 rpm for 4 hours, themethanol solvent was subsequently removed by drying, and then PPE powderwas recovered by screening through a JIS test sieve with an aperture of12 μm.

After placing 210 parts by weight of toluene and 2.6 parts by weight ofpolystyrene in a separable flask, they were stirred at 25° C. todissolve the polystyrene. Next, 53.3 parts of previously prepared PPEpowder was added and the mixture was stirred at 25° C. for 2 hours toobtain a dispersion of PPE particles. The obtained PPE dispersion wasused to obtain prepreg H with a resin content of 60 mass %, by the samemethod as Example 2.

Example 9

Prepreg I with a resin content of 60 mass % was obtained by the samemethod as Example 8, except that the aperture of the JIS test sieve waschanged to 20 μm.

Example 10

Prepreg J with a resin content of 60 mass % was obtained by the samemethod as Example 8, except that the aperture of the JIS test sieve waschanged to 26 μm.

Example 11

After placing 158 parts by weight of toluene in a separable flask, itwas heated to 80° C. After then adding 53.3 parts of PPE1 and 1.5 partsby weight of polystyrene, the mixture was stirred at 80° C. for 2 hoursto dissolve the PPE and polystyrene. Stirring was halted, and thetemperature was lowered to 25° C. over a period of 5 hours to obtain adispersion of PPE particles. When the dispersion was observed under anoptical microscope, approximately 4 to 12 μm PPE crystalline particleswere found to be dispersed.

After adding 22.8 parts by weight of triallyl isocyanurate and 1.5 partsby weight of α,α′-bis(t-butylperoxy-m-isopropyl)benzene to the obtainedPPE dispersion and uniformly stirring, 19.8 parts ofdecabromodiphenylethane was added and the mixture was uniformly stirredto obtain a coating varnish.

The obtained varnish was then impregnated into an E glass cloth with athickness of about 0.1 mm (2116 STYLE, product of Asahi-Schwebel Co.,Ltd.), and after wiping off the excess varnish with a slit, the solventwas removed by drying to obtain a prepreg K with a resin content of 60mass %.

The proportion (particle number %) of primary particles with particlesizes of between 3 μm and 20 μm in the prepreg was 68%.

Example 12

Prepreg L with a resin content of 60 mass % was obtained by the samemethod as Example 11, except that the temperature lowering of thetoluene solution of PPE and polystyrene was to 35° C.

The proportion (particle number %) of primary particles with particlesizes of between 3 μm and 20 μm in the prepreg was 92%.

Example 13

Prepreg M with a resin content of 60 mass % was obtained by the samemethod as Example 11, except that the amount of toluene was 210 parts byweight, and the temperature lowering of the toluene solution of PPE andpolystyrene was to 20° C.

The proportion (particle number %) of primary particles with particlesizes of between 3 μm and 20 μm in the prepreg was 81%.

Example 14

Prepreg N with a resin content of 60 mass % was obtained by the samemethod as Example 13, except that the temperature lowering of thetoluene solution of PPE and polystyrene was to 35° C.

The proportion (particle number %) of primary particles with particlesizes of between 3 μm and 20 μm in the prepreg was 88%.

Example 15

After placing 147 parts by weight of a toluene/methanol mixed solvent(mass ratio: 95:5) in a stainless steel beaker, 32.3 parts of PPE1 and3.6 parts by weight of a styrene-based elastomer were added whilestirring, and stirring was continued for 2 hours. Next, a homomixer(Model HM-300 by As One Corp.) was used for shredding of the PPE underconditions of 25° C., 8,000 rpm for 30 minutes, to obtain a dispersionof PPE particles.

Next, 21.3 parts by weight of triallyl isocyanurate and 2.3 parts byweight of α,α′-bis(t-butylperoxy-m-isopropyl)benzene were added to theobtained PPE dispersion and the mixture was uniformly stirred, afterwhich 15.9 parts of decabromodiphenylethane and 24.6 parts by weight ofsilica were added and the mixture was uniformly stirred to obtain acoating varnish.

The obtained varnish was then impregnated into an E glass cloth with athickness of about 0.1 mm (2116 STYLE, product of Asahi-Schwebel Co.,Ltd.), and after wiping off the excess varnish with a slit, the solventwas removed by drying to obtain a prepreg 0 with a resin content of 60mass %.

Example 16

PPE1 was mashed with a mortar and then screened using a JIS test sievewith an aperture of 38 μm, and the screened portions were recovered toobtain PPE powder.

After placing 210 parts by weight of toluene and 2.6 parts by weight ofpolystyrene (650, by PS Japan Corp.) in a separable flask, they werestirred at 25° C. to dissolve the polystyrene. Next, 53.3 parts ofpreviously prepared PPE powder was added and the mixture was stirred at25° C. for 2 hours to obtain a dispersion of PPE particles. When thedispersion was observed under an optical microscope, PPE particles withlong diameters of approximately 2 μm to 40 μm were found to bedispersed. The obtained PPE dispersion was used to obtain prepreg P witha resin content of 60 mass %, by the same method as Example 2.

Comparative Example 1

After placing 158 parts by weight of toluene in a separable flask, itwas heated to 80° C. After then adding 53.3 parts of PPE1 and 2.6 partsby weight of polystyrene, the mixture was stirred for 2 hours todissolution. After then adding 22.8 parts by weight of triallylisocyanurate and 1.5 parts by weight ofα,α′-bis(t-butylperoxy-m-isopropyl)benzene and uniformly stirring, 19.8parts of decabromodiphenylethane was added and the mixture was uniformlystirred to obtain a coating varnish.

The temperature of the obtained varnish was then lowered to 60° C. whilestirring, and impregnated into an E glass cloth with a thickness ofabout 0.1 mm (2116 STYLE, product of Asahi-Schwebel Co., Ltd.) underconditions maintaining the varnish at 60° C., and after wiping off theexcess varnish with a slit, the solvent was removed by drying to obtaina prepreg Q with a resin content of 60 mass %.

Comparative Examples 2, 3 and 5

Prepregs R, S and U with resin contents of 60 mass % were obtained bythe same method as Example 2, except for using the formulations listedin Table 1.

Comparative Example 4

After placing 280 parts by weight of toluene in a separable flask, itwas heated to 80° C. After adding 53.3 parts of PPE1, 2.6 parts byweight of polystyrene and 22.8 parts by weight of triallyl isocyanurate,the mixture was stirred at 80° C. for 2 hours to dissolution. Stirringwas halted, and the temperature was lowered to 25° C. over a period of 5hours to obtain a dispersion of PPE particles. When the dispersion wasobserved under an optical microscope, approximately 0.2 to 8 μm PPEcrystalline particles were found to be dispersed.

After adding 1.5 parts by weight ofα,α′-bis(t-butylperoxy-m-isopropyl)benzene to the obtained PPEdispersion and uniformly stirring, 19.8 parts of decabromodiphenylethanewas added and the mixture was uniformly stirred to obtain a coatingvarnish.

The obtained varnish was then impregnated into an E glass cloth with athickness of about 0.1 mm (2116 STYLE, product of Asahi-Schwebel Co.,Ltd.), and after wiping off the excess varnish with a slit, the solventwas removed by drying to obtain a prepreg T with a resin content of 60mass %.

Test Example 1

Each of the prepregs A to U obtained in the examples and comparativeexamples were evaluated. The results are shown in the table.

TABLE 1 Example Example Example 1 Example 2 Example 3 Example 4 Example5 Example 6 Example 7 Example 8 Example 9 10 11 Curable Polyphenyleneether 1 32.3 53.3 53.3 42.6 53.3 53.3 53.3 53.3 resin Polyphenyleneether 2 53.3 composition Polyphenylene ether 3 53.3 Partial maleatedpolyphenylene ether 53.3 (Mn 18,000) Low molecular weight terminalbenzylated 10.7 polyphenylene ether (Mn 2,400) Low molecular weightterminal allylated polyphenylene ether (Mn 2,600) Low molecular weightterminal partially allylated polyphenylene ether (Mn 2,600) Lowmolecular weight polyphenylene ether (Mn 3,000) Triallylisocyanurate21.3 22.8 22.8 22.8 22.8 22.8 22.8 22.8 22.8 22.8 22.8 Polystyrene 2.62.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 Styrene-based elastomer 3.6 Silica24.6 Decabromodiphenylethane 15.9 19.8 19.8 19.8 19.8 19.8 19.8 19.819.8 19.8 19.8 α,α′-bis(t-Butylperoxy-m- 2.3 1.5 1.5 1.5 1.5 1.5 1.5 1.51.5 1.5 1.5 isopropyl)benzene Extraction Insoluble (A) Polyphenyleneether 95 93 92 96 89 92 90 88 93 94 87 by content (wt %) specificNumber-average mol. 18,000 18,000 18,000 25,000 10,000 18,000 17,00018,000 18,000 18,000 18,000 solvent wt. Percentage of particles 99 99 9999 99 99 99 99 99 99 100 with sizes: 0.3-200 μm (particle %) Percentageof particles 99 99 99 99 99 99 99 99 79 66 100 with sizes: 1-100 μm(particle %) Percentage of primary 99 100 99 99 99 99 99 99 99 98 100particles with sizes: 0.3-30 μm (particle %) Percentage of primary 98 9998 98 97 96 98 98 94 88 99 particles with sizes: 0.3-20 μm (particle %)Percentage of primary 86 88 66 90 89 70 90 89 82 88 29 particles withsizes: 0.3-3 μm (particle %) Maximum size (μm) 5 6 7 6 5 7 5 8 12 18 12Soluble (B) Average mol. wt. 18,000 17,000 18,000 23,000 10,000 14,00017,000 18,000 18,000 18,000 18,000 (A) and (B) mass ratio 88:12 88:1292:8 92:8 87:13 69:31 72:28 88:12 90:10 92:8 74:26 Prepreg name A B C DE F G H I J K Property Permittivity Steady state 3.5 3.6 3.6 3.6 3.6 3.63.6 3.6 3.6 3.6 3.6 (10 GHz) Moisture absorption 3.5 3.6 3.6 3.6 3.6 3.63.6 3.6 3.6 3.6 3.6 state Dielectric loss Steady state 0.0065 0.00500.0050 0.0045 0.0053 0.0048 0.0046 0.0050 0.0050 0.0051 0.0050 tangent(10 GHz) Moisture absorption 0.0077 0.0059 0.0059 0.0053 0.0061 0.00580.0055 0.0060 0.0061 0.0062 0.0065 state Permittivity (1 GHz) 3.6 3.63.6 3.6 3.6 3.6 3.6 3.6 3.6 Dielectric loss tangent (1 GHz) 0.003 0.0020.002 0.002 0.002 0.002 0.002 0.002 0.002 Prepreg powder fall-off andpeeling G G G G G G G G G G G (180°) Prepreg powder fall-off and peeling(90°) G G G G G G G G G G G Absorption (wt %) 0.19 0.20 0.27 0.29 0.150.25 0.25 0.30 0.32 0.34 0.21 Soldering heat resistance 288° C. 288° C.288° C. 288° C. 288° C. 288° C. 288° C. 288° C. 288° C. 288° C. 288° C.Copper foil peel strength (N/mm) 1.8 1.9 1.7 1.8 1.9 1.8 1.9 1.7 1.7 1.71.8 Example Example Example Example Example Comp. Comp. Comp. Comp.Comp. 12 13 14 15 16 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Curable Polyphenyleneether 1 53.3 53.3 53.3 37.6 53.3 53.3 53.3 53.3 resin Polyphenyleneether 2 composition Polyphenylene ether 3 Partial maleated polyphenyleneether (Mn 18,000) Low molecular weight terminal benzylated polyphenyleneether (Mn 2,400) Low molecular weight terminal allylated 42.6 53.3polyphenylene ether (Mn 2,600) Low molecular weight terminal partially53.3 allylated polyphenylene ether (Mn 2,600) Low molecular weightpolyphenylene 10.7 ether (Mn 3,000) Triallylisocyanurate 22.8 22.8 22.837.6 22.8 22.8 22.8 22.8 22.8 22.8 Polystyrene 2.6 2.6 2.6 2.9 2.6 2.62.6 2.6 2.6 2.6 Styrene-based elastomer Silica Decabromodiphenylethane19.8 19.8 19.8 17.8 19.8 19.8 19.8 19.8 19.8 19.8α,α′-bis(t-Butylperoxy-m- 1.5 1.5 1.5 4.1 1.5 1.5 1.5 1.5 1.5 1.5isopropyl)benzene Extraction Insoluble (A) Polyphenylene ether 96 90 10088 98 — — — 60 — by content (wt %) specific Number-average mol. 18,00018,000 18,000 18,000 18,000 — — — 18,000 — solvent wt. Percentage ofparticles 100 100 100 — 82 — — — 100 — with sizes: 0.3-200 μm (particle%) Percentage of particles 100 100 100 — 65 — — — 100 — with sizes:1-100 μm (particle %) Percentage of primary 100 100 100 — 97 — — — 99 —particles with sizes: 0.3-30 μm (particle %) Percentage of primary 99 9999 — 55 — — — 99 — particles with sizes: 0.3-20 μm (particle %)Percentage of primary 7 18 12 — 11 — — — 35 — particles with sizes:0.3-3 μm (particle %) Maximum size (μm) 12 13 12 — 36 — — — 12 — Soluble(B) Average mol. wt. 16,000 17,000 16,000 18,000 18,000 18,000 2,5002,700 17,000 2,500 (A) and (B) mass ratio 59:41 70:30 45:55 85:15 74:260:100 0:100 0:100 78:22 0:100 Prepreg name L M N O P Q R S T U PropertyPermittivity Steady state 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 (10GHz) Moisture absorption 3.6 3.6 3.6 3.6 3.7 3.6 3.7 3.7 3.7 3.7 stateDielectric loss Steady state 0.0051 0.0051 0.0050 0.0072 0.0058 0.00520.0053 0.0054 0.0052 0.0060 tangent (10 GHz) Moisture absorption 0.00660.0066 0.0066 0.0085 0.0073 0.0072 0.0082 0.0082 0.0084 0.0080 statePermittivity (1 GHz) 3.6 3.6 3.6 3.6 Dielectric loss tangent (1 GHz).002 0.002 0.002 0.004 Prepreg powder fall-off and peeling G G G G P P PP P P (180°) Powder Peeling Peeling Peeling Powder Peeling fall-offfall-off Prepreg powder fall-off and peeling (90°) G G G G G P P P P PPeeling Peeling Peeling Powder Peeling fall-off Absorption (wt %) 0.270.20 0.31 0.33 0.46 0.35 0.45 0.48 0.43 0.41 Soldering heat resistance288° C. 288° C. 288° C. 288° C. Unacceptable 260° C. 260° C. 260° C.Unacceptable 260° C. Copper foil peel strength (N/mm) 1.8 1.8 1.7 1.70.8 1.5 1.5 1.5 1.1 1.0 Polyphenylene ether 1: S202A, Asahi KaseiChemicals Corp., number-average mol. wt. 18,000, average no. phenolichydroxyl groups per molecule: 1.84 Polyphenylene ether 2: S201A, AsahiKasei Chemicals Corp., number-average mol. wt. 25,000, average no.phenolic hydroxyl groups per molecule: 1.84 Polyphenylene ether 3:S203A, Asahi Kasei Chemicals Corp., number-average mol. wt. 10,000,average no. phenolic hydroxyl groups per molecule: 1.84Triallylisocyanurate: Nihon Kasei Co., Ltd. Polystyrene: 650, PS JapanStyrene-based elastomer: SOE L606, Asahi Kasei Chemicals Corp. Silica:Spherical silica, Tatsumori, Ltd. Decabromodiphenylethane: SAYTEX8010,Albemarle Japan Corp. α,α′-bis(t-Butylperoxy-m-isopropyl)benzene:PerbutylP, NOF Corp.

Based on the results in Table 1, the prepregs of the examples all had nopowder fall-off or peeling of the resins, and excellent handleability,compared to the prepregs of the comparative examples.

In addition, the copper-clad laminates and laminated sheets obtainedfrom the prepregs of Examples 1 to 15 all had higher copper foil peelstrengths and more excellent water absorption resistance, soldering heatresistance and electrical characteristics compared to the comparativeexamples. Furthermore, as regards the electrical characteristics, therewas low variation in the steady state and the moisture absorption state,and the stability was excellent. The cured products had excellentadhesion (interlayer peel strength in the multilayer boards, or peelstrength between the cured curable resin compositions and the metalfoil, such as copper foil).

The copper-clad laminate and laminated sheet obtained from the prepregof Comparative Example 1, wherein the prepreg was produced usinghigh-molecular-weight PPE particles but in a dissolved state so that PPEparticles did not remain in the prepreg, had somewhat poorer copper foilpeel strength, water absorption resistance and soldering heat resistancecompared to the copper-clad laminates and laminated sheets obtained fromthe prepregs of Examples 2, 3 and 8 to 15 which had the same resincomposition. The electrical characteristics in the steady state werealso equivalent, but the electrical characteristics in the moistureabsorption state were reduced.

The copper-clad laminates and laminated sheets obtained from theprepregs of Comparative Examples 2, 3 and 6, wherein low molecularweight PPE was used so that PPE particles did not remain in the prepreg,had somewhat poorer copper foil peel strength, water absorptionresistance and soldering heat resistance compared to the copper-cladlaminates and laminated sheets obtained from the prepregs of Examples 1to 15. The electrical characteristics in the steady state were alsoequivalent, but the electrical characteristics in the moistureabsorption state were reduced.

The copper-clad laminate and laminated sheet obtained from the prepregof Comparative Example 5, wherein the PPE content in the PPE particles(A) was low at 60%, had poorer copper foil peel strength, waterabsorption resistance, soldering heat resistance and electricalcharacteristics compared to the copper-clad laminates and laminatedsheets obtained from the prepregs of Examples 2, 3 and 8 to 14 which hadthe same resin composition.

Test Example 2

Table 2 shows the evaluation results obtained using a copper foil with athickness of 12 μm and a surface roughness Rz of 2.0 μm (FV-WS foil,product of Furukawa Electric Co., Ltd.) as the copper foil.

TABLE 2 Prepreg B Prepreg R Prepreg S Prepreg P Prepreg U Prepreg OGlass 205 196 192 202 210 215 transition temperature (° C.) Interlayerpeel 1.2 0.9 0.7 0.7 0.4 1.0 strength (N/mm) Copper foil 0.9 0.7 0.7 0.40.6 0.8 peel strength (N/mm) Peel strength 1.3 1.3 1.0 1.8 0.7 1.3 ratioDielectric loss 0.0049 0.0052 0.0052 0.0053 0.0058 0.0052 tangent [10GHz] CTE (ppm/K) 40 50 45 50 40 75 Heat resistance SatisfactorySatisfactory Satisfactory Delamination Satisfactory Satisfactory testCross-sectional Satisfactory Satisfactory Satisfactory — CrackingCracking observation near copper near base after heat foil materialresistance test

The laminated sheet using prepreg P had a low copper foil peel strengthof 0.4 N/mm, and failed to satisfy the requirements for a laminatedsheet of the second mode, while the results of cross-sectionalobservation indicated that delamination of the copper foil had occurredin the heat resistance test.

The laminated sheet using prepreg U had a copper foil peel strength ofgreater than 0.6 N/mm, but the interlayer peel strength was low at 0.4N/mm, which was only 0.7 times the copper foil peel strength, and itfailed to satisfy the requirement of a peel strength ratio of between0.8 and 1.8 for the laminated sheet of the second mode, while theresults of cross-sectional observation also showed cracking of the resinnear the copper foil.

The laminated sheet using prepreg 0 had a large CTE of 75 ppm/K andfailed to satisfy the requirements for a laminated sheet of the secondembodiment, while the results of cross-sectional observation showedcracking of the resin near the copper foil.

INDUSTRIAL APPLICABILITY

Because adhesion between the PPE-containing curable resin compositionand the base material is satisfactory, it is possible to provide aprepreg for an electronic circuit board that can yield a cured producthaving low resin dust fall-off and resin flaking during production andhandling, as well as excellent adhesion by hot pressure molding (forexample, interlayer peel strength for multilayer boards, or peelstrength between cured curable resin compositions and metal foils suchas copper foils), moisture absorption resistance, heat resistance andstability of electrical characteristics under hygroscopic conditions,and it can be suitably used for production of an electronic circuitboard comprising a cured product of the prepreg.

Furthermore, since the prepreg has excellent adhesion betweenlow-dielectric resins and low-roughness metal foils, there is no peelingor blistering of the copper foil during production and handling and alow-roughness metal foil may be used to obtain satisfactory transmissioncharacteristics, and it can be suitably used in a layered material foran electronic circuit board that has minimal peeling of the basematerial sections or resin cracking near the base material or metal foilduring production and handling.

In addition, even when a low-dielectric resin with a dielectric losstangent of no greater than 0.007 is used, the laminated sheet is ahighly reliable laminated sheet that is resistant to cracking underthermal load, moisture absorption load and mechanical load, and it canbe suitably used as an electronic circuit board.

1-23. (canceled)
 24. A laminated sheet comprising a low-dielectric resinand a base material, wherein: (1) the dielectric loss tangent of thelaminated sheet at 10 GHz is no greater than 0.007 (cavity resonancemethod), (2) the metal foil peel strength of the laminated sheet with ametal foil that has a side with a surface smoothness of no greater thanRz 2.0 μm is 0.6 N/mm or greater, (3) the coefficient of linear thermalexpansion of the laminated sheet (≦Tg) is between 20 ppm/K and 60 ppm/K,and (4) the peel strength between the low-dielectric resin and the basematerial is between 0.8 and 1.8 times the metal foil peel strength. 25.A laminated sheet according to claim 24, wherein the Tg of the laminatedsheet is 180° C. or higher.
 26. A laminated sheet according to claim 24,wherein the thickness of the metal foil is less than 35 μm.
 27. Alaminated sheet according to claim 24, wherein the metal foil peelstrength of the laminated sheet with a metal foil that has a side with asurface smoothness of no greater than Rz 2.0 μm is 0.8 N/mm or greater.28. A laminated sheet according to claim 24, wherein the peel strengthof the laminating material with the low-dielectric resin and the basematerial is 0.6 N/mm or greater.
 29. A laminated sheet according toclaim 24, wherein the ratio between the peel strength of the laminatedsheet with the low-dielectric resin and the base material, and the metalfoil peel strength (base material-resin/metal foil ratio) is between1.05 and 1.8.
 30. A laminated sheet according to claim 29, wherein theratio between the peel strength of the laminated sheet with thelow-dielectric resin and the base material, and the metal foil peelstrength (base material-resin/metal foil ratio) is between 1.3 and 1.8.31. A laminated sheet according to claim 24, wherein the low-dielectricresin comprises polyphenylene ether (PPE) at between 10 mass % and 70mass % based on 100 mass % as the low-dielectric resin.
 32. A laminatedsheet according to claim 31, wherein the PPE has a number-averagemolecular weight of between 1,000 and 7,000, and the average number ofphenolic hydroxyl groups per PPE molecule is between 0.1 and 0.8.